DNA blunder let Night Stalker continue

These included three elderly women who were raped and 20 more who were sexually assaulted.

A series of mistakes led to Grant being ruled out as a suspect after a burglary in Bromley when the DNA of a second man with the same name was confused with his.

The error meant successive teams of detectives did not reconsider whether Grant could be the vicious sex attacker.

Two years later, in March 2001, a friend of Grant called police after recognising an e-fit on BBC1's Crimewatch.

The informant, who had links with a children's home in Bromley, named Grant and the first name of a second man, and said one of them resembled the e-fit.

But detectives did not make any further inquiries as his name was accompanied by a "code one" DNA elimination notice on the police database.

The long-running police inquiry was plagued by several red-herrings, including suspicions that Grant rode a motorbike and that he was from the Windward Islands.

Commander Simon Foy, head of the Met's homicide and serious crime command, apologised to Grant's victims for failing to stop him in 1999.

Mr Foy said: "In 1999 there was an opportunity to have identified and apprehended Grant but that opportunity was missed.

"When this came to light after his arrest we voluntarily referred this matter to the Independent Police Complaints Commission (IPCC).

"It is entirely appropriate for the Met to apologise for this missed opportunity that led to his continued offending for so long afterwards.

"We are deeply sorry for the trauma suffered by all those victims and our failure to bring Grant to justice earlier."

The IPCC launched an inquiry after the concerns of senior Scotland Yard officers were passed to them in February last year.

The May 1999 blunder followed a night-time raid on the home of an elderly woman in Bromley, south-east London.

The burglary, in which the woman was not sexually assaulted, had some of the hallmarks of a Night Stalker case but was handled by local officers.

Several days later, a neighbourhood watch co-ordinator contacted police to say she saw a black man putting on gloves and walking towards the house.

The eyewitness passed the registration number of a BMW car to police and this was traced to Delroy Grant's wife Jennifer at their Honor Oak home.

A police officer made a search using the name "Delroy Grant" on the police national computer to see if any convicted criminals were likely suspects.

She identified six people, including a Delroy Grant who lived in Hackney and whose last offence was a burglary in Dulwich.

A detective alerted to the lead visited the Grant family home and spoke to Mrs Grant, but her husband was out and no further action was taken.

Meanwhile, a DNA swab was taken from the Hackney suspect and somehow this was confused with Delroy Grant's record, ruling him out of the Night Stalker inquiry.

One source said the DNA mistake was "simply human error" compounded by the structure of the police database which meant the result was never questioned.

He said: "Grant was eliminated without anyone actually seeing him. The crime report ends at that point with no result and no outcome."

Questions remain over the 2001 Crimestoppers call as the caller said he recognised Grant through a childrens' home, although Grant was never a resident at one.

Police spent a significant amount of time trying to identify the home, only to discover the building and all records in it had been destroyed in a fire.

Detective Superintendent Simon Morgan, who led the inquiry from 2001, said the call would not have led police to Grant.

He said: "Looking at what happened to that information at the time and what we now know, that information was completely incorrect."

For several years police suspected Grant rode a motorcycle to his crimes and included the information in their public appeals.

This was based on the fact he wore a biker-style boilersuit with Velcro collar and cuffs, biker-style gloves and a balaclava.

One victim also claimed she heard the distinctive exhaust note of a motorcycle soon after he struck in 1990.

But detectives now believe the noise she heard was the unusual sound of a big-engined American TransAm car Grant owned at the time.