Practicas de laboratorio

Forensic Cases: Colin Pitchfork, First Exoneration Through DNA
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One of the keystones of forensic science is DNA testing. DNA (deoxyribonucleic acid) is the genetic material present in every cell. Each individual has a unique DNA profile. There are even a few differences between the DNA of identical twins.
A British scientist, Sir Alec Jeffreys, developed DNA profiling in the 1980s. DNAfor profiling can be extracted from samples of human cells found at a crime scene, including blood, semen, skin, saliva, mucus, perspiration and the roots of hair, and profiling can even be carried out on old and dried out samples.
The case of Colin Pitchfork was the first murder conviction based on DNA profiling evidence (there was a previous rape conviction based on this type of evidence) – andthe first exoneration as well.

The Exoneration

After going missing, Lynda Mann, a 15-year-old schoolgirl, was raped and murdered in the grounds of Carlton Hayes psychiatric hospital in Narborough, Leicestershire, in November 1983. Forensic examination of semen sample showed that it was a type found in only 10% of men, and was from someone with type A blood.
However, the police did not find asuspect. In 1986, another 15-year-old schoolgirl, Dawn Ashworth, was similarly sexually assaulted and strangled in the nearby village of Enderby, and semen samples showed the same blood type.
Richard Buckland, a local 17 year old with learning disabilities who worked at Carlton Hayes psychiatric hospital, had been spotted near Dawn Ashworth’s murder scene and knew unreleased details about thebody. He confessed to Dawn Ashworth’s murder but not Lynda Mann’s.
Using Sir Alec Jeffreys’ new technique, scientists compared the semen samples with a blood sample from Richard Buckland. This proved that both girls were murdered by the same man, and also proved that this man was not Richard Buckland – the first person to be exonerated using DNA.

The Conviction

In 1987, in the first ever massDNA screen, the police and forensic scientists screened blood and saliva samples from 4000 men aged between 17 and 34 without an alibi in the villages of Enderby and Narborough and nearby Littlethorpe. The turn out rate was 98%, but the screen did not find any matches to the semen samples. The police and scientists expanded the screen to men with an alibi, but still did not find a match.
InAugust 1987, a woman overheard a colleague, Ian Kelly, boasting that he had given a sample posing as a friend of his, Colin Pitchfork. Colin Pitchfork had persuaded Ian Kelly to take the test as he claimed he had already given a sample for a friend who had a flashing conviction. The police arrested Colin Pitchfork in September 1987, and scientists found that his DNA profile matched that of themurderer.
Colin Pitchfork had previous convictions for flashing, and claimed that the murders had begun as flashings, but the girls had run away, which had excited him.
In January 1988, Colin Pitchfork was sentenced to life imprisonment for the murders, and was told he had to serve a minimum of 30 years.

Forensic Cases: The M25 Rapist, Antoni Imiela

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In March 2004, a judge at MaidstoneCrown Court sentenced Antoni Imiela, a 49-year-old Briton of German and Polish origin to seven life sentences for the rape of seven women and girls aged 10 to 52 in Kent, Surrey, London and Hertfordshire, with a further 29 years for the kidnap, indecent assault, and attempted rape of a 10-year old girl in Birmingham. As most of the crimes took place around London and the Home Counties, the press namedhim the ‘M25 Rapist’.
Imiela’s convictions were based on evidence from the women and girls, and on forensic evidence from a number of disciplines.
According to the Forensic Science Service, the search for Imiela was the biggest linked police enquiry since the hunt for the Yorkshire Ripper.

DNA Evidence

The first attack was in November 2001, when a 10-year-old girl was kidnapped from...