The prosecution of Rachel Nickell’s killer was delayed by almost two years because of human rights concerns about obtaining a sample of his DNA, a senior government official said yesterday.

Prosecutors were concerned that Robert Napper’s lawyers might claim a violation of his human rights if his DNA were taken without his proper consent while he was a mental patient, according to the legal official.

In 2006 Lord Goldsmith, then attorney-general, was informed of the debate about Napper’s rights. Lawyers finally concluded that a DNA sample could lawfully be taken.

The official said: “Human rights was one of the arguments that stopped them getting his DNA. The Crown Prosecution Service and the police decided they had to resolve it because it could have been a technicality that could have collapsed the trial.”

At the Old Bailey last week Napper admitted killing Nickell, a part-time model, on Wimbledon Common in 1992. He was returned to Broadmoor where he was already serving an indefinite sentence for the horrific killing of Samantha Bissett, 27, and her four-year-old daughter Jazmine in 1993.

The Metropolitan police admitted both women and the child might still be alive were it not for a series of failings by detectives. The Met issued an unprecedented apology to the families of all three victims.

Police initially ignored the trail to Napper, focusing instead on Colin Stagg, who was acquitted in 1994. It was to be 10 years before a break-though in forensic techniques meant scientists were able to isolate a tiny fragment of DNA taken from Nickell’s body.

Within weeks scientists had established that it matched a sample from Napper which had been taken in the 1990s and held on the DNA database.

Napper has been linked to a total of 109 sex offences and 86 possible victims. He is also likely to be quizzed by police about the killings of at least three other women: Claire Tiltman, who was stabbed 40 times in Greenhithe, Kent, in 1993; Penny Bell, 43, who was knifed 50 times in Greenford, west London, in 1991; and Jean Bradley, 47, who was stabbed in Acton, west London.

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