|Suspect(s):||Colin Stagg - acquitted, Robert Napper - convicted of manslaughter on grounds of diminished responsibility|
Re-investigation revealed unknown male DNA on samples from Rachel’s body.
On 15th July 1992, while walking with her young son and their dog on Wimbledon Common in London, Rachel Nickell died after suffering no fewer than forty-nine separate stab wounds at the hands of serial rapist Robert Napper.
Among other things, adhesive-tape samples were taken from parts of her body that had been exposed during what looked like a sexually motivated attack. When these were examined for DNA by scientists at the Metropolitan Police Forensic Science Laboratory (MPFSL), the hope was that they would find male DNA that didn’t match either Rachel’s husband or their two-year-old son.
The problem in this case was that not only did the scientists fail to find any of the male DNA they were looking for; they didn’t find any DNA at all. It seems that they didn’t stop to wonder why. If they had, they would have realised something was wrong, because the tape should have been covered in with Rachel’s own DNA and skin cells.
After interviewing several suspects, the attention of the Metropolitan Police focused on a local man named Colin Stagg. Convinced that Stagg was guilty, but with no real evidence to implicate him, they organised a so-called ‘honey trap’ operation. For several months an undercover policewoman feigned a romantic interest in Stagg, with the aim of getting him to confess to Rachel’s murder.
Ultimately, although Colin Stagg didn’t ever ‘confess’ to the murder, he was arrested in August 1993. A year later, at his trial at the Old Bailey, the judge excluded the entrapment evidence, the prosecution withdrew its case, and Stagg was acquitted for the crime.
In 2002, when Forensic Alliance became involved in the cold-case investigation into Rachel’s murder – which was given the code name Operation Edzell – Angela Gallop assigned Roy Green to the case, assisted by several colleagues. Mike Gorn focused on the chemistry aspects of the case, while Clare Lowrie was responsible for hairs and textile fibres. Andy McDonald took care of DNA analysis, and April Robson was appointed lead forensic examiner.
The first thing we did was look at the items of clothing that had been retrieved from her and from her two-year-old son, Alex.
Next, we examined the body samples and the tapings taken from her body. Semen is traditionally a good source of DNA, but since the previous scientific team hadn’t found any semen on Rachel’s body, we anticipated that we’d be looking for smaller traces. Then, in phase three, we looked at various items that had been collected from the crime scene on Wimbledon Common and from some potential suspects. Later on we added a fourth phase, which involved looking more closely at the debris the FSS had gathered from key items.
To assist with the first phase of our investigation – our search for ‘foreign DNA’ that could have come from Rachel’s attacker – Roy set up a reconstruction experiment in the laboratory. The aim was to try and identify the specific areas of Rachel’s clothes that were most likely to have been handled by her attacker. Another scientist put on clothes (over a scene suit) that were similar to the clothes Rachel had been wearing at the time of her attack. Then Roy – acting as the attacker and with black powder applied to his hands – pulled and pushed them until they resembled the distribution of Rachel’s clothing when her body was discovered.
Residues of black powder indicated where contact had been greatest, and therefore where on her clothes we should focus our attention. Then we started work on phase two – which was when we found a ‘way in’ to the case.
When the previous scientific teams had tested the tapings from Rachel’s body, they’d used a DNA-profiling test called Low Copy Number (LCN). LCN is a variation on the standard DNA (STR) profiling used at the time that works by multiplying (or amplifying) relevant parts in small amounts of DNA until there is enough present to analyse. With LCN, thirty-four cycles of amplification were used, as opposed to the twenty-eight with the standard test.
Our team took a different approach. We always began with the standard (twenty-eight-cycle at that time) test, so that we had a baseline of what our extracts contained in the way of DNA. We only progressed to the LCN test if we felt it was appropriate.
When we looked at the tapings extract from the previous tests, what we found using the standard method of twenty-eight cycles was a mixed profile. The major component appeared to be from Rachel herself, while some minor components were from a male. When we then tested the same extract using a thirty-four-cycle LCN technique – the equivalent of the previous test – it was clear that our reaction was over-amplified, leading to an excess of DNA and no result.
Intrigued by the tiny amount of male DNA, we went back to the original intimate tapings and re-sampled them, creating our own extracts. We then repeated the same testing as before. With some of the tapings we got a full profile from Rachel, and although there was something else there, it wasn’t confirmed by the duplicate test. With other tapings, however, even at twenty-eight cycles we were getting a major result from Rachel and a minor result from male DNA, but not enough to identify who it might have originated from.
We decided this was the ideal opportunity to take a different approach. It involved cleaning up and concentrating our sample extracts: trying to eliminate as much extraneous material such as salts and impurities as possible, because they can inhibit DNA analysis. We then tweaked the running conditions on our machines to optimize the process.
Our colleagues at Orchid Cellmark undertook the bulk of this work, with Roy making sure it was done as quickly as possible because we needed to continue to make progress with this case. In the end, it took the better part of two years. Andy McDonald then carried out some other DNA tests on our extracts from the intimate tapings, in an effort to obtain as much information from them as possible. By the end of it all, we had plenty of information with which to mount a search of the National DNA Database.
Roy Green had noticed at quite an early stage of the investigation that there were similarities between the modus operandi (MO) – that is, a criminal’s pattern of behaviour or his/her way of committing a crime, and that of a man called Robert Napper. Napper had been incarcerated in Broadmoor Hospital since 1995 for the murder of another young woman and her four-year-old daughter. When the DNA extracted from the samples in our investigation was put on the National DNA Database, he came up as a match.
We then began to search for more links. One of the places we looked was on some of Napper’s possessions that had remained untouched at Broadmoor since they’d been returned to him by police a few years earlier. Police investigators had apparently been particularly interested in a red-painted toolbox, about which Napper was very protective. It was of further interest to us after we found a tiny flake of red paint in some hair combings from Rachel’s son. And when Mike Gorn compared the paint flake with the paint on the toolbox, he got a match. Additionally, a layer of metal on one side of the flake was shown to be steel – which was what the toolbox was made of.
We were still thinking about the crime scene and whether there was anything there that might conceivably provide a link to Napper. One of the things we considered was a couple of footwear marks that had been found in mud on a bridle path close to where Rachel had been attacked. Casts had been made out of the marks at the time, one of which was the heel of a shoe that was similar in style to the heel of a pair of Napper’s shoes, but slightly smaller in size.
Since the mark was different from the suspected source, we had to find out if there was a good reason, and the only way to do this was to return to the scene and conduct an experiment. Shortly afterwards, Mike and Roy found themselves on Wimbledon Common looking at what happened when a similar pair of shoes was used to walk over the same area of muddy ground. What they found was that as the wearer of the shoes lifted his foot to take another step, a partial vacuum was created that sucked in the muddy soil around the edges of the shoe. And when they took the plaster-type casts of the marks and compared them with the shoes themselves, they showed that what was left in the mud was a slightly smaller footprint than would normally have been made by a shoe of that size.
In the face of what had turned out to be overwhelming evidence – including the DNA, the paint and the footwear mark – Robert Napper pleaded guilty when the case went to trial. In December 2008, he was convicted of the manslaughter of Rachel Nickell on the grounds of diminished responsibility and sentenced to indefinite incarceration at Broadmoor hospital.
Professor Angela Gallop and the team are currently working on a number of high profile cold case investigations. To find out more about our services visit our forensic services page or call 01235 774870.