The ‘eureka’ moment that revolutionised crime solving

Image credit: Anita Corbin and John O'Grady, British Council 1989

The ‘eureka’ moment that revolutionised crime solving

The ‘eureka’ moment that revolutionised crime solving

In 1984, Alec Jeffreys developed the technique of DNA fingerprinting in his laboratory at the University of Leicester. These techniques have revolutionised the way that the police solve crimes.

The ‘eureka’ moment that revolutionised crime solving

From the dining table to the lab

From a young age Alec Jeffreys was fascinated by science and the world around him. Aged eight, he received his first chemistry set and from then on he was always experimenting!

Fast forward 19 years and Alec was in charge of his own, albeit small, genetics laboratory at the University of Leicester. It was an exciting time for science in the 1970s. Alec had considerable freedom in his lab and made full use of it, often staying at the lab long into the small hours – much to the annoyance of his wife, Susan.

Humans share around 99.9 per cent of their DNA.

Alec and his team” were studying inherited variation and had shifted their focus from the products of genes, specifically blood groups, to DNA itself. As humans we share around 99.9 per cent of the same genetic material. But what Alec was interested in was the remaining percentage, the part that contains our unique genetic code. Alec wanted to find this code and understand it. However, to do this was a bit like looking for a single letter difference in two, otherwise identical, books.

Seal with a stutter

Alec identified a repeating sequence or ‘stutter’

Alec started by examining the DNA sequence found in the myoglobin gene of seals. Myoglobin is an oxygen-binding protein found in muscle tissue. It is essential to diving mammals like seals and whales that need to swim to great depths in order to feed. The myoglobin enables them to hold oxygen in their bodies for long periods of time. The myoglobin gene has developed and adapted over millions of years, mice have a similar gene, and so do we. Within the DNA sequence of the seal myoglobin gene Alec identified a repeating sequence or ‘stutter’ in the sequence. He realised that these stutters were unique to an individual and therefore could be used to distinguish one seal from another. Perhaps similar sequences in humans could be used to distinguish one person from another.

Minisatellites are short, 10-60 base pair sequences of repetitive DNA that show greater variation from one person to the next than other parts of the genome.

The scientific name for these stutters is a minisatellite. These are short, repetitive sequences of DNA, (usually 10 to 60 base pairs long), that occur at more than 1,000 locations throughout the human genome. Minisatellites are highly variable so tend to differ from person to person, which means that by comparing minisatellites it is possible to identify a particular individual.

Alec needed to take a closer look at the stutter before he could understand it fully. So he tried to cut the DNA up into smaller and smaller pieces using specific enzymes. But time after time he came up against a wall – the enzymes weren’t cutting the DNA as much as he hoped. This meant he wasn’t able to get a clear picture of the stutter.

A page from Alec Jeffreys’ notebook showing notes on the protocol used for the first DNA fingerprint.
Image credit: Science Museum, London, Wellcome Images


Alec had a saying ‘every failure leads to success’, so he kept on working. In September 1984 he decided to try something different based on his knowledge of the myoglobin gene. He took a DNA sample from one of his lab technicians and placed it alongside DNA from their mother and father as well as the DNA from a tobacco plant, a cow and a seal.

Probes are small fragments of DNA tagged with radioactive phosphorous that only attach to complementary pieces of DNA in the genome.

Alec used a radioactively-labelled probe that would help him to recognise the myoglobin gene. A probe is a short segment of DNA that can be used to help find specific sequences of bases in a DNA molecule. In short, the probe only binds to the DNA sequence you are looking for and highlights it as a black blob or band. It was by using this probe that Alec finally had his eureka moment at 9:05 am on 10 September 1984.

What Alec found was that the probe had bound to all the minisatellite sequences that had a similar sequence to his probe. This resulted in a pattern of dark bands that was completely unique to the individual. The technician shared parts of their pattern with their mother and father showing that they were related. In contrast, the tobacco, cow and seal all had completely different patterns, showing that they were not related at all. Finally, the penny dropped and Alec realised he had produced the first DNA fingerprints.

The first DNA fingerprint. The first three lanes contain DNA from a woman, her mother and her father respectively. The other lanes contain DNA from other species including cow, grey seal and tobacco. The DNA probe used detected minisatellites whose length varies between individuals.
Image credit: Alec Jeffreys, Wellcome Images

Bringing families back together

The news of Alec’s accidental eureka moment soon reached the press. In 1985 Alec was approached to help with an immigration case by a lawyer who had read about DNA testing in The Guardian.

The lawyer was representing a Ghanaian family, the mother of which had been living in the UK for some time with two of her children. Her remaining child had recently arrived in Britain but had been accused of having a fake passport and was at risk of being permanently sent back to Ghana.

After discussions with the lawyer, Alec took a sample of blood from the mother and the boy she claimed was her son, as well, as her other children. He then extracted their DNA and compared their genetic fingerprints. The fingerprints showed that not only was the boy definitely the mother’s son, but that he was related to her other children as well. As a result the Home Office dropped the case and the boy was permitted to stay in the UK with his family. For the first time a legal dispute was resolved with the help of results from a genetic test.

Killer at large

Meanwhile, just after midnight on 21 November 1983, a 15 year old girl called Lynda Mann was reported missing in Narborough near Leicester. She had headed off earlier in the evening to visit a friend but had failed to return. A few days later her body was found on a deserted foot path, known locally as the Black Pad. She had been raped and murdered just 300 metres from her home.

The investigation into Lynda’s murder was led by Detective Chief Superintendent David Baker. He made a promise to Lynda’s mother that he would find the man who killed her daughter. He moved his team” into an unused cricket building in Narborough to help investigate the case and show support to the local community.

A year later however, they were still no closer to finding the killer despite hundreds of leads and the belief that the assailant was a local man.

On 31 July 1986 David received a call he had been dreading. Another young girl had been reported missing after visiting a friend. Dawn Ashworth was found 14 hours later in a wooded area near a footpath called Ten Pound Lane. She had been raped and murdered just like Lynda had been three years earlier.

A local man claimed he had known the whereabouts of Dawn’s body before the police did

Not long after Dawn was found, a local 17-year-old man claimed he had known the whereabouts of Dawn’s body before the police did. David and his colleagues arrested him on suspicion of rape and murder of the two girls and took him to the station for questioning. The suspect openly confessed to attacking and killing Dawn but claimed he had nothing to do with Lynda’s murder. But something didn’t quite add up. Some of the details that had been given by the suspect did not fit with the crime scene of Dawn’s murder.

David was keen to find concrete proof that the suspect was involved in both cases to confirm his suspicion that it was the same man that had murdered both girls. They had a hair sample from Lynda, plus a semen sample found on her clothes that was believed to have come from her killer. Surely there must be some way to prove or disprove whether this suspect was responsible?

Genetics holds key to solving the crime

David had read about a local scientist from the University of Leicester who had been working on the use of DNA analysis to resolve immigration and paternity disputes. He got in contact with Alec Jeffreys who was prepared to help with the case but wasn’t sure if the samples from Lynda, taken three years previous, would still be viable for DNA testing. Despite this, he went ahead anyway. A blood sample was taken from the suspect and compared to the two DNA samples from Lynda. The results showed that the suspect’s DNA was completely different from the DNA in the sample found on Lynda’s clothes. So he was telling the truth, he hadn’t killed Lynda. But was he responsible for Dawn’s murder?

Alec carried out the same test, this time with a semen sample taken from Dawn’s body. Again there was no match between the suspect’s DNA and that found on Dawn’s body. So the DNA evidence suggested he didn’t murder either girl despite his confession. He became the first person to have his innocence proven by DNA fingerprinting. Further analysis showed that the DNA samples on both murder victims were the same. So, without a doubt, the same man had murdered both Lynda and Dawn.

Back to square one?

According to research, serial killers tend to kill within a five mile radius of where they live. Spurred on by the effectiveness of Alec’s DNA fingerprinting test David had a brilliant idea – to test the DNA from every man between the ages of 18 and 34 who lived within an 8 kilometre radius of where the bodies were found. This would be about 5,000 men in total. It would be labour-intensive, time-consuming, expensive and an entire new forensic facility would be needed. But David was determined to find the killer before he had a chance to repeat his crime a third time.

The Home Office were initially reluctant to pay for the test

Before they could go ahead with the DNA tests they needed backing from the government. At over £100 for each blood test they would need around £500,000 to go ahead. The Home Office were initially reluctant to pay for the test despite extensive talks with Alec and David. Eventually, with the support of the Prime Minister, Margaret Thatcher, the project was given the go-ahead. Now they just had to convince local men to come forward for the tests.

DNA ‘manhunt’

Every man between the ages of 18 and 34 who lived within a five mile radius of where the victims’ bodies were found was asked to attend their local station to give a small sample of blood. Anyone who refused to attend or ignored the invitation were visited by the police and asked why. On the whole however, turnout was surprisingly good.

Alec predicted that only around 1,000 of the 5,000 samples would go through to the full genetic test. They knew that the murderer had type A blood so they would only have to do a full test on men who also had type A blood. However, it was likely that the process would still take about five months to complete.

Unfortunately at this time, Alec Jeffreys became unwell with glandular fever. Ironically, he had visited the doctor with suspected flu and refused a blood test to confirm the diagnosis. Luckily the DNA analysis labs that had been set up at the Home Office Forensic Science Service in Aldermaston, continued to process the samples whilst he recovered.

The head of the police department started to have doubts as to whether the process was actually working

By the time 4,007 samples had been taken, with 3,100 men cleared, the head of the police department started to have doubts as to whether the process was actually working. There were serious talks about stopping funding for the DNA investigation and admitting defeat. In addition to this, Alec’s wife Susan was concerned about the implications her husband’s involvement in a very public murder case might have on their family. At this point Alec was very much in the public eye and was still being approached for immigration and paternity cases, with some people even coming directly to the house to ask for his help.

Bringing the killer to justice

On 16 September 1987 the police department got a call from a young woman who had overheard someone bragging in a Leicester pub that he’d given a blood sample to the investigation on behalf of someone else.

The man was Ian Kelly. Ian worked at the Hampshires Bakery in Leicester alongside his friend Colin Pitchfork. Colin, who had moved to Leicester away from Narborough a month after Lynda was murdered, asked Ian to provide a DNA sample on his behalf. Wanting to keep his job and his friend, Ian had agreed. As a result Colin was able to evade being part of the DNA testing and avoid being investigated by the police.

They had finally found their man and could prove he was guilty

On hearing this confession, the police immediately brought Colin Pitchfork in for a DNA test. Sure enough, the DNA profiles of Colin Pitchfork and the murderer were an exact match. They had finally found their man and with his DNA profile they could prove in black and white that he was guilty.

Colin Pitchfork received two life sentences for the murders of Lynda Mann and Dawn Ashworth. His workmate, Ian Kelly, received an 18 month sentence, which was suspended for two years, for conspiring to pervert the course of justice. If it hadn’t been for the DNA samples and Alec Jeffreys’ revolutionary DNA fingerprinting discovery, it is unlikely that Colin Pitchfork would have been caught as quickly as he was. DNA fingerprinting is the most important contribution to forensic science since the original fingerprint and has been an invaluable tool in the fight against crime, enabling police across the world to identify criminals and bring them to justice.

Modern-day DNA profiling relies on microsatellites, or short tandem repeats (STRs), rather than the minisatellites used in DNA fingerprinting.

Although the technology used to catch Colin Pitchfork is now largely obsolete, the DNA fingerprinting techniques developed by Alec Jeffreys have been improved to make the whole process much more accurate and efficient.

Deservedly, Alec Jeffreys’ work has received widespread recognition. He was elected as a Fellow of the Royal Society in 1986, awarded the title of Honorary Freeman of the City of Leicester in 1993 and knighted in 1994 for services to genetics. He retired in September 2012 and continues his association with the University of Leicester as an Emeritus Professor.

Sir Alec Jeffreys who developed the DNA fingerprinting technique.
Image credit: Public Library of Science

Now retired, Detective Chief Superintendent David Baker was also acknowledged for his role in solving the murders of Lynda Mann and Dawn Ashworth. He received The Queen’s Police Medal for his distinguished career of over 40 years in the police service. After all, it was his decision to contact Alec Jeffreys all those years ago that has resulted in the use of DNA profiling to solve crimes today.

The UK National DNA Database contains DNA profiles from over 5 million individuals.

Today we have a national DNA database holding the genetic profiles from all convicted criminals and it is arguably one of the most powerful tools we currently have in the fight against crime.

This page was last updated on 2016-06-13

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