A RAPE IN the public toilets of a Co Cork town last year was shocking in its brutality. Old-fashioned police work and science combined to identify the stranger who attacked the woman, and forensic scientists in Ireland’s real-life CSI lab were instrumental in securing a conviction through DNA evidence.
“CSI Dublin” is located in the Phoenix Park, and hosts specialists in chemistry, drugs and DNA. They handle 10,000 cases a year.
Forensic scientist Stephen Clifford works in the area of serious crime. On a typical day, blood-stained clothing, guns or body fluids linked to murders, attempted murders or assaults might arrive on Clifford’s lab bench.
“Some of the detail in the cases is pretty horrific. You try assess it from a purely scientific view,” says Clifford, “and it helps that you can’t visualise the people. Then you go home and look at the news and there’s a slant on it. You see the pictures and it makes it more real. In the lab, it is better to be detached from it.”
In the Cork case, scientists initially could not find blood, skin cells or semen or other forensic evidence. “We thought it was going to be a dead-end,” says Clifford, who was one of the scientists assigned to the case.
The attacker was later identified and arrested at home and forensics revealed that DNA under his nails and on clothes in his house matched those of the victim.
DNA typically can be recovered from blood, hair, semen and skin cells. The TV series CSI: Crime Scene Investigation is on the money when it comes to DNA’s importance. DNA persists for a long time and its use has revolutionised forensic science, says Louise McKenna, director of science at the Forensic Science Laboratory.
But TV programmes wrongly suggest forensics can solve everything, she says, and sometimes there is no DNA at all. In one published study, DNA was found to be transferred only around 30 per cent of the time when a firearm was handled, for example.
“Those [CSI] guys seem to be policemen, scientists and lawyers all wrapped into one,” says Clifford, almost enviously, “and the lab is like a nightclub.”
“The speed at which people get results and the certainty of their conclusions are completely unrealistic,” says McKenna.
In the real world, context is all-important in DNA evidence. “The evidence is strong in relation to the match, but the question is ‘what does it mean?’” says McKenna.
Something that’s slowly gaining favour is evaluative expert opinion. This applies statistical reasoning to subjective probabilities. It could, for example, give the degree of likelihood that a mark had been made by a certain item of footwear.
The idea is to give the jury, police or lawyers an indication of what the evidence means in a particular context, McKenna explains. In a domestic incident, DNA is often not so important because there can be lots of innocent explanations for the presence of DNA.
However, if an assailant claims never to have met a victim, even a tiny amount of biological material can link the assailant to victim and crime.
In the case of Swiss student Manuela Riedo, who was murdered in Galway in October 2007, DNA evidence was recovered from a condom not far from her body. The DNA on the outside linked it to the victim, whereas the DNA profile inside helped identify and convict her killer.
McKenna says forensic scientists in the Phoenix Park labs worked through the night on items brought from that murder scene. “We knew if we could generate DNA from these items, it would help progress the case, which it did,” she adds.
It’s not all about DNA though. The lab also studies drugs, explosive residues, fibres, firearm residue and fire debris. Forensic scientist Amanda Lennon works in chemistry and deals with trace evidence, mainly paint and glass, and footwear impressions.
In a case where a man was shot through a window in Bray, up to eight forensic experts went to work, checking clothes recovered near the scene for firearm residues and DNA.
Glass was also collected and sent to the lab. Lennon explains what happens next: “A scene-of-crime officer would take a sample from all windows broken at the scene and secure the samples in packages. If they apprehend a suspect within a reasonable time frame, they take their outer clothing and package the garments carefully to avoid contamination.”
The clothes are brushed over a specialised funnel in the lab and the debris is collected in a Petri dish at the bottom. Magnified 40 times, the debris is examined for glass under a microscope and pieces are counted.
Glass evidence typically arises in cases of burglary, criminal damage, intimidation, assault and hit-and-run cases. Glass can differ according to its refractive index (how it bends light) and how it was treated.
Paint can be examined under a microscope and its chemical structure determined using infrared techniques. In a recent hit-and-run, paint taken from a suspect van linked it to the crime scene.
Some criminals may have become forensically savvy, but scientific techniques are improving too. In the early days, a €2-coin-size blood patch was needed for DNA. Now, commercial kits extract DNA from as few as a couple of dozen cells, Clifford says.
Even bones give up their secrets. Bone has very little DNA, says Clifford, and it can degrade over time or when exposed to water or the by-products of decomposition. But the lab recently identified a man killed in the 1980s by generating a DNA profile from his bones, and a murder investigation was opened up. In macabre but essential work, DNA profiles can be generated to help identify bodies found at sea, with DNA extracted from muscle tissue or from ground-up bone marrow.
The lab hopes to see a DNA database in place soon. “It would be extremely useful,” says McKenna, “and has proven very successful in other countries.” Typically, such databases would hold the profiles of anyone suspected of committing a crime warranting imprisonment.
Cutting, cooking and chemical fingerprints
KRISTEN O’CONNOR holds up a clear, sealed-evidence bag of drugs. Within it can be seen a smaller bag of drugs, depicting black rabbits. “This is a possession case – amphetamines,” the forensic scientist says.
The arrival and opening of the bag are meticulously recorded and the sample analysed in a gas chromatograph. This splits the substance into its various compounds and generates a read-out which can be compared to a library of chemicals. “We got a positive here for amphetamine and there is a whole bunch of other stuff too,” says O’Connor.
The “chemical fingerprints” of common “cutting agents” or additives pop up on the screen as distinctive graphs.
“Paracetamol is added to heroin, so when you ‘cook it up’ it bubbles,” she explains. “In cocaine, you will also detect benzocaine and lidocaine, local anaesthetics. Smell the cocaine and your nose numbs, so it seems a stronger mix than it really is.”
Looking at the graphs, she points to a form of sugar, which bulks up drugs such as cocaine. Caffeine sometimes is added too. The scientists had their own noses to the grindstone during the headshop era, when synthetic variants of drugs which were difficult to identify were common.
“There was a massive influx of drugs and a lot of them where unknowns,” says O’Connor. “Some of them are still floating around, but they are becoming less prevalent.”
