China, Criminal Justice and Evidence

   I'm back, and this time I'm using this post as a sort of awareness raiser about China's legal system, it's going to be a little opinion-y and a little less science-y but hopefully you'll find it interesting enough to read around and form your own opinions.

   Currently China not only convicts 99.9% of its suspects but it also hands out the death sentence more prolifically than every other legal system in the world combined. While this is a shocking statistic the most important question here is why such a high percentage of suspects are convicted. Either China's police force is made up almost entirely of Sherlock level detectives, or, possibly more credibly, there is something at play here that's heavily skewing the system in favour of the prosecution. It has been claimed that wrongful conviction, tat may be responsible for the absurdly high figure, could be due to given orders and sloppy police work. However China hardly stands alone in suffering from this unprofessional conduct within its judicial system. What really makes the difference in my opinion is the massive credibility given to forced confessions (a slight euphemism for torture until they confess), and the fact the police, who are invariably prosecuting, have complete control of the evidence.

     Now eye witness reports are shaky at best, worse when lead by a skilled lawyer, the fact any credibility is given to that extracted by hanging a person upside down and going to town on their stomach with a hammer is something that would have made even the Roman's blush.

   This becomes an un-fightable one-two punch against the defence once you realise that the defence is not entitled to any of the crime scene evidence. The prosecution can pick and choose evidence that supports their case, making an objective approach to understanding what happened at a crime scene impossible.

   Imagine for example that investigators discover a woman dead in her home due to assault with a blunt instrument. They discover blood spatter from repeated attacks suggesting a man roughly the height of the husband, however the spatter suggests left handed swings when the husband was right handed and also that the only blood on the husbands clothes has large fragments of clots in it, so must be from hours after the crime. Now the police can't find another suspect apart from the husband so they build a case against him. They can simply include that blood is concordant with a man his height and the wife's blood was found on his clothes, leaving out the considerable evidence against their case. Obviously this makes defending near impossible.

    Luckily China is beginning to address the issue, due to mounting internal and external pressure on its judicial system. A recent example of this is the case of Nian Bin in which a grocery store owner was accused of murdering his neighbours by poisoning their porridge with rat poison. The police managed to extract a confession from Nian Bin by torture. Nian was convicted and sentenced to death. However in a series of legal battles, with his sister leading the defence with the aid of a former judge, many holes in the prosecutions argument where uncovered. For example, the man who the police claimed had sold Nian the poison not only looked nothing like Nian's description of him but also did not even sell the type of poison the toxicology report claimed had been used. Also while Nian confessed to having laced the kettle used to boil water for porridge with the poison, not everyone who ate the poison fell sick, whereas everyone who ate the squid did.

   Possibly the most damning thing however was that around 11 minutes into the interrogation video the camera angle shifts, and Nian suddenly appears to be on the verge of crying, and immediately begins to confess to murders, where he had been silent and unresponsive before. Logs of the interrogation found by the former judge suggested a 2 hour gap around this time in which the interrogators had tortured Nian, and allegedly threatened to torture his wife.

    While the highly successful defence team, built upon Chinese lawyers who saw the failure of the current judicial system, they only managed to win Nian retrial after retrial. Judges, lawyers and police hate having cases overturned. It reflects very badly on them, and will destroy their reputation as well as make any promotion much more difficult, and as the retrials are usually conducted in the same court the judge and prosecutors are likely to be those involved in the original case. Nian received four death sentences, and may never have been exonerated (making it into the lucky 0.1%) if it weren't for the fact that recently the Chinese legal system has been heavily embarrassed by having to throw out a murder conviction after the supposed victim reappeared alive over a decade later (Zhang Aiquing, 1994), a case in which confession extracted by torture had been pivotal.

   Cases like this had lead to a revision of the Chinese criminal procedure which allowed the defence team to question the police in court as well as call in their own expert witnesses. One of these expert witnesses happened to be a forensic scientist from Hong Kong, who noticed that the spectrometer slides of the victim's blood were in fact all from the same sample, just with different labels. As if this wasn't bad enough, the conclusions of the report had been written before the results came through, showing that the police had likely forged the results to fit their case.

   This lead to one of the first repealed death sentences in the Chinese judicial system not based on supposedly dead people reappearing alive, or on incontrovertible DNA evidence, but rather on good forensic science and a logical argument.

   While some may see this as a depiction of the corruption and failure of the system, I think it can also be seen as cause for hope. It shows that with enough perseverance logic and evidence are starting to have a place in the Chinese courts, and in addition it shows that many of those high up in the Chinese legal system, for example the former Lawyer who aided the defence as well as many lawyers who aided pro bone, are willing to fight against corruption. In fact Shen Deyong, one of china's most senior judges recently called for more respect for the legal system from those within it. In his words:

"It's preferable to release someone wrongfully, than convict someone wrongfully," he said. "If a true criminal is released, heaven will not collapse, but if an unlucky citizen is wrongfully convicted, heaven will fall."

While I'm not sure how much I agree with this I think it's indicative of general movement of those within the Chinese Judicial system in the right direction. It's something that will hopefully lead to a decrease in the illogical and often barbaric nature of many investigations and possibly result in a less bloody court in general. 

Thanks for reading! Until next time, over and out!

Non-Newtonian Fluid Behaviour and Blood Spatter

It's been a while but we're back with the field of blood spatter analysis. This is, in my opinion, one of the most interesting fields, and hopefully you think so too!

Blood typically behaves pretty strangely for a liquid. For a long time blood was considered as only a Newtonian fluid. A Newtonian fluid can be described as one where liquid drops form due to surface tension and can oscillate during flight away from their source. However Non-Newtonian fluids form by virtue of internal cohesion and are extremely stable in flight.

Blood's interesting because it can either act Newtonian or non-Newtonian depending on victim's condition and the type of injury.

Let's start with Newtonian fluids. The principles used to define Newtonian fluids are taken from his Principia, which say: "The resistance that arises from the lack of (viscosity) of the parts of the liquid, other things being equal, is proportional to the velocity with which the parts of the liquid are separated from one another". Newtonian flow is mainly dependant upon a viscosity constant and surface tension, where each is proportional to the rate of flow. As shown by the equation:

tau=mu*(dv/dy)

Tau = shearing or frictional stress per unit area against the walls of the containing vessel or the enveloping air around a drop, this is called a Reynolds number.

Mu = Coefficient of viscosity, it is a constant of proportionality

dv/dy = A linear change in velocity gradient of flow

So a higher Reynolds number means a fluid is more viscous fluid.

Non-Newtonian fluids, however, follow the formula:

tau=kappa*(dv/dy)^n

Where kappa is a constant but not of viscosity, as the viscosity is no longer a constant. While the shear rate (friction) is constant at any given velocity, it changes depending on the flow rate, which now equals a changing velocity gradient: (dv/dy)^n. The change is now exponential, rather than linear. Tau now refers to the Deborah number, rather than the Reynolds number. It is named after the biblical quote from Deborah: “Everything flows before the lord”. This is because non-Newtonian fluids follow the principle that everything flows given enough time.  Non-Newtonian fluids generally flow much more slowly than Newtonian fluids as the shear (friction) against their path of flow is considerably greater (exponential not linear).

Blood normally behaves as a non-Newtonian fluid as its flow is not evenly distributed but is in fact formed of a core of red blood cells, surrounded by a layer of white blood cells, which in turn are surrounded by a platelets scattered through plasma (axial flow). This type of flow is stable when your bloods flowing normally. However when there are high rates of flow, or in stressful situations, the body shifts water into the veins, disrupting the axial flow and converting the blood to a Newtonian fluid. As we now know, Newtonian fluids are less viscous and less stable. Essentially the blood becomes turbulent.

So why are we interested in this in the first place? Well first of all some organs in the body (for example the brain and adrenal glands) receive Newtonian blood all of the time. This means by looking at blood spatter evidence, and the proportion to which it acts as Newtonian or non-Newtonian can locate where the blood spatter pattern comes from.

The most obvious difference in blood spatter patterning is that Newtonian fluid spatters causes small, dense central circle with a fine satellite spatter, whereas non-Newtonian is more likely to project streaks outwards from the central circle.

Anyway, this has all been very maths-y, but hopefully interesting! Over and out, and until next time!

DNA Profiling: Polymerase Chain Reaction

We're back to the murky world of DNA forensics, the first technique on the agenda is the polymerase chain reaction.  The polymerase chain reaction is an enzymatic process that facilitates the isolation and amplification of a specific sequence of DNA, without affecting the surrounding regions. When the quality of the DNA sample available to you is so limited in both quantity and quality,as it so often is in forensics, the importance of this technique sky rockets.

Without further ado, here's the protocol:
 1. Sample is incubated at 94-97˚c to separate the DNA helix into two separate strands by denaturing the DNA.
 2. Reduce the temperature to 50-60˚c to allow primers to 'anneal' (recombine into) to the DNA.
 3. Raise the temperature to 70-72˚c to initiate a polymerisation step, where an enzyme called Taq DNA polymerase utilises the DNA template identified by the primers to create a complimentary strand to the template.
 4. This sequence is repeated so that the original sequence is quickly amplified a thousand fold.
 5. After amplification the PCR products (amplicons) are separated on the basis of their length. The technique used to do this is known as capillary electrophoresis. Capillary Electrophoresis separates samples based on the velocity of their attraction to an oppositely charged electrode. Since DNA has a slight negative charge, the velocity of attraction increases with chain length.

The primer design for this process is extremely important. They a short strands of DNA that will hybridise onto the beginning and end of the are you want to analyse. The primers are also labelled with fluorescent dyes. This allows PCR products to be detected when exposed to a fluorescence inducing laser. This is recorded by a camera and allows the DNA produced to be quantified in real time. Once sufficient DNA has been produced it can be used for analytical techniques such as sequencing or southern blotting.

Short Tandem Repeat Marker analysis is the cornerstone of DNA forensics, however it can only be used with sufficient amounts of a specific genome. This can be determined using the fluorescence analysis technique described above, in combination with a TaqMan probe. A TaqMan probe is a protein that displaces part of a DNA strand, but cleaves when the synthesis enzyme reaches it, cleaving into a reporter dye and quencher dye. Now that the reporter and quencher die are no longer in close proximity (i.e. bound to each other), the reporter die fluoresces.

Given the comparatively hardcore science nature of this post I'm going to give your brains a rest and leave the fun that is STRs,sequencing and southern blotting for another time! Over and Out.

Introduction to DNA Profiling

Here we are, the technique considered by many to be a holy grail of forensics. But what is DNA profiling and how does it work? Well first things first, the term DNA profiling refers to the sequencing of an individuals DNA. 

When DNA profiling there are 3 possible outcomes:

1. Exclusion - the sample DNA does not match the suspects, thus ruling them out. This can be used to prove innocence or rule out suspects.

2. Inconclusive - due to damage through contamination or DNA degradation, further information must be sought, and the test must be carried out again.

3 Inclusion - The DNA is a match. However as DNA is not unique the significance of the match is calculated by quantifying the random match probability (Pm)'. The (Pm)' is a statistical test that estimates the probability of two unrelated people sharing the same DNA profile. Where markers are not linked (so inherited independently), the (Pm)' can be estimated by multiplying individual allele frequencies within a sample population. Therefore the more loci that are included in the analysis and the greater their heterozygosity the smaller the value of (Pm)' will be. A smaller (Pm)' means that the DNA being profiled is more likely to have come from the suspect. 

Despite DNA profiling's high levels of specificity there are a few problems with the technique. The first is that DNA will degrade over time, meaning it is harder to produce conclusive results with the test. The second major problem is that DNA from related people is extremely similar so has a much higher (Pm)' value. This means in cases between family members DNA is much less useful.

We'll end the introduction with a quick case study:

   1983, a girl in Narborough, Leicestershire is found dead with sigs of rape. A semen sample recovered from her body was tested and showed that the murderer was blood group A and had an enzyme profile shared by about 10% of the male population. However this was the only evidence recovered, and the investigation made no progress.

   1986, a second girl in the same area, was also found raped and murdered. The semen sample recovered from the body showed the same characteristics as the one from the case 3 years ago. The police established this connection between the 2 cases. The police believed that they were the work of the same man and that he lived in the vicinity. Their investigation led them to Richard Buckland, who was arrested. When interrogated he confessed to the second girls murder but denied having any involvement in the first. Buckland was DNA profiled, as were the semen samples. The girls had in fact been killed by the same man, but this man was not Buckland. 

   Having lost their primary suspect the police tried a different approach. They conducted the first ever mass DNA screening. All men in the vicinity (roughly 5000) had a blood sample or saliva swab taken. From these those exhibiting a matching enzyme profile and blood group where then DNA profiled. However despite all this they had nothing. There were no matches. Once again the investigation hit a wall. 

    Six months later however a woman reported that she had overheard a man claiming to have provided DNA in place of his friend, Colin Pitchfork. Colin Pitchfork was subsequently dragged in, and his DNA profile, unsurprisingly, was a match, inclusive. By 1988 he had been sentenced to life in prison. 

Colin Pitchfork on his arrest

   This case study helps show how DNA evidence alone is rarely enough to find or convict a suspect, but is very effective at excluding suspects. Thanks for reading! I'll be back soon, and we're going to be getting into some harder science! Over and Out!

Testing for Blood

You've probably all seen it in TV dramas; the crime scene looks clean as a whistle, not a trace left. That is until the CSI unit rolls in, sprays a mysterious liquid all over the place, off go the lights, out come the UV lamps and suddenly the room is covered in ethereal blue stains. Well you may be happy to learn that that's one of the few things that forensics shows largely get right.

Presumptive tests for blood reveal blood where it may not have been found with the naked eye. This could be due to it blending well with the background, seeping into cracks, or possibly just occuring in trace amounts. Luckily presumptive tests can help a forensic scientist find and identify blood at a crime scene.

Presumptive tests for blood are usually based on haemoglobin's ability to catalyse the oxidation of certain reagents. The most common reagent is Hydrogen Peroxide Solution (H202(aq)). These tests also commonly use reagents that change colour on oxidation. Phenolphthalein which goes from colourless to pink when oxidised.

To test a stain, a small circular piece of absorbant card (diameter=25mm) is folded twice to form a point. A small amount of the stain being tested is then scraped onto this point. a drop of phenophlthalein is added by a drop of hydrogen peroxide, with the bright pink colour showing a positive result. It's important to note that this test does not differentiate between human blood and other kinds of blood. 

However in some situations the colour change tests are not appropriate. Maybe the crime scene has been scrubbed clean, or you need the blood 'intact' for DNA profiling. This is were luminol comes into play. In the luminol test an alkaline solution containing both luminol and an oxidising agent (for example Hydrogen Peroxide), is sprayed onto the area being tested. Where blood is present luminol is catalytically oxidised and produces a distinct glow. 

Luminol before and after

I hope this has helped to illuminate the basics of blood identification. Until next time! Over and out!

Immunoassays in the Analysis of Drugs and Poisons

I'm back, and this time we're going to be looking at one of the most powerful techniques in the toxicologists arsenal, the immunoassay. No matter the sample size or the specificity or broadness of molecules your trying to ferret out, the immunoassay is both practical, accurate and relatively cheap.

In forensics the immunoassays are used mainly for identifying the presence of drugs in or poisons in both ante and post mortem samples. Immunoassays can be highly specific, picking out only a single compound (e.g. mephamphetamine), or a group of compounds. Immunoassays are useful because not only are they highly sensitive, they are also able to analyse large samples relatively quickly and require no preliminary extraction phase.

Immunoassay relies on the antibody-antigen reaction, which occurs in the mammalian immune system. When an antigen enters the body, an antibody specific to it i produced. The antibody binds with the antigen forming an antigen-antibody complex. In immunoassays specific antibodies are used to detect and measure the level of the analyte of interest.

In immunoassays, fixed quantities of the specific antibody to the analyte and a labelled form of that sample are added to the sample being tested. The labelled molecules and the analyte (if it's present) will competitively attempt to bind with the antibodies, in inversely proportional numbers. So you can measure the reduction in concentration of the labelled poison to work out the concentration of a drug in the sample. 

However in some types of immunoassay, it isn't possible to distinguish between the labelled poison bound to the antibody and that remaining free in solution, so physical separation of the two phases is required before measurement. These are known as heterogenous immunoassays (for example radioimmunoassay). However immunoassays where this is not necessary are called homogenous immunoassays (for example fluorescence polarisation immunoassay). These two examples are actually both very good examples of immunoassays. 

Radioimmunoassays: In radioimmunoassays, the poisonous molecules are labelled with an appropriate radioisotope (for example iodine-125) and the radioactivity is measured. The concentration of unlabelled poison molecules in the test mixture is determined by reference to a standard curve. This graph is produced by adding increasing concentrations of poison to a fixed quantity of labelled poison and antibodies. 

Fluorescence Polarised Immunoassays: A suitable fluorescent substance is used to label the analyte. It's possible to distinguish between labelled analytes bound to the antibody and analytes free in solution. This is because the former emits polarised fluorescence, but the latter generates unpolarised fluorescence.

Thanks for reading, over and out!

Jamaica ginger and 'The Jake Leg'

The Jake Leg was an epidemic found primarily during the early 20th Century in 'dry' America. America in the early 20th Century was place rife with poison and one of the places that forensic since was born. The Jake Leg however was not a symptom of poisons employed by malicious murderers or ignorant architects, rather something people induced themselves. As the astute of you may have guessed this this is symptom of bootlegged alcohol poisoning, namely a type called Ginger Jake. Ginger Jake was the dry alcohol for the poorer folk in South America, who could not afford properly, illegally distilled alcohol.

Those readers who are not experts on prohibition America (what weirdos right?) may be asking what the jake leg was. The jake leg was in fact a particularly nasty symptom of ginger jake poisoning. The jake leg was in fact a partial paralysis, which was usually severe enough to force the sufferer to walk in a foot slapping, high stepping style. 

The Jake Leg was actually caused tri-orthocresyl (TOCP). Tri-orthocresyl is an organophosphate which is used as a solvent in industry (a plasticiser), especially in aircraft oil. It causes peripheral neuropathy, degeneration of the peripheral nerves, inhibiting communication between brain and extremities. 

This effect is primarily due to the reaction between TOCP and a particular enzyme in the nerves (it acts as an enzyme inhibitor). The TOCP enzyme complex then goes through a process known as ageing. The reaction with the protein occurs rapidly (taking roughly an hour), however the neuropath takes much longer to become evident (10 days at least). This is because the enzyme which is inhibited by TOCP is essential to nerve cell function. Therefore in the long cells in the arms and legs the nerves die progressively. This entails a degeneration of the myelin sheathe and nerve working upwards towards the spinal cord. 

Dry America was a dangerous place for many reasons, with radon in water, thallium in make up and TOCP in alcohol. Toxicology is the science that put a stop to this. It doesn't just ensure that murderers are brought to justice but helps to protect everyone from exposure to some of the deadliest chemicals out there. 

That concludes todays post, until nest time! Over and out.