Forensic test flaws may have affected many cases' outcome

London: Dangerous criminals including killers and rapists may have escaped justice because of blunders by forensic scientists, it has been revealed.

As many as 2,000 criminal cases are being urgently reviewed, among them the murder of Rachel Nickell, amid fears that crucial DNA evidence was missed.

Differences in the way forensic laboratories tested for DNA samples between 2000 and 2005 may have meant vital evidence slipped through the net.

Crucially, it emerged on Wednesday that the Government-owned Forensic Science Service was not using the latest techniques.

The Association of Chief Police Officers wrote to all police forces in England and Wales on Wednesday asking them to carry out a review of their serious crime cases.

One of the most prominent cases involved is that of the murder of Nickell in 1992. Forensic scientists who reviewed the case in 2001 are now believed to have missed vital evidence that could have identified the killer.

Nickell, 23, was stabbed 49 times and sexually assaulted in front of her two-year-old son Alex on Wimbledon Common. A key suspect, Colin Stagg, was charged and acquitted of murder after police were accused of trapping him into a "confession".

However, if scientists had found tiny traces of DNA they could have identified the real killer.

Detectives are preparing to charge a second man, a convicted sex killer detained at Broadmoor.

The Home Office asked the Association to conduct a review of the issue last year but news of the development has only begun to emerge, leading to claims that there has been an attempt at a cover-up.