The Night Stalker: it took 17 years to make an arrest

When police in South London began to investigate a particularly brutal rape of an elderly woman in 1992, they never imagined that it would be the best part of two decades before a breakthrough was made in what had become one of the biggest and most complex cases in Scotland Yard's history.

By the time Delroy Grant, 52, was arrested in a targeted raid on Sunday morning, the 'Night Stalker' had committed well over 100 attacks on lone women aged between 68 and 88, including five rapes and another 30 indecent assaults. 

The true figure may never be known, but officers involved with the hunt for Britain's most prolific sexual predator, codenamed Operation Minstead, believe that a significant number of the Night Stalker's victims were so devastated that they could not bring themselves to report it to the police.

Those who did summon up the courage to do so were often too traumatised to provide coherent accounts of their ordeal or detailed descriptions of their attacker, who usually broke into their homes after dark, disguising himself with a balaclava, and never left a fingerprint. Piecing together the scanty accounts, police concluded they were looking for an athletically built black man aged between 24 and 45.

But although the attacker had left his DNA at the scene of several crimes, there was no match on the UK's national DNA database, which contains samples from anyone arrested since 1995.   

Faced with an initial list of some 21,000 "persons of interest", the Minstead team managed eventually to whittle down the number of possible suspects to around 900, largely through voluntary DNA testing. In a bid to reduce this further, a Florida company specialising in ancestral profiling using DNA "markers" was commissioned to investigate the Night Stalker's origins. After the research indicated that his parents probably came from the Windward Islands, several Minstead officers were despatched to conduct voluntary DNA tests on local people for purposes of comparison.

At the same time, a prominent forensic psychologist, Dr Julian Boon, was brought in to develop a profile of the attacker: he concluded that the Night Stalker was a "gerontophile", somebody who, in the inverse of a paedophile, had a powerful sexual attraction to elderly women.

Boon warned the Minstead investigators that although the Night Stalker was capable of remorse - he spared some of the women he targeted from rape and halted one attack when the victim asked what his mother would think of his conduct - his sexual urges would eventually lead to a death.

That almost occurred during a horrific assault that left an 88-year-old women with severe internal injuries from which she was never entirely to recover. Dr Boon subsequently parted company abruptly with the Minstead team, in circumstances that remain unclear: one account  suggested the Night Stalker may have had made contact with him but that he had not informed the police of this (Boon has never spoken about this publicly).

According to police sources, after a long period of inactivity, the attacker had recently become "blasé", seemingly so confident of his ability to escape justice that he reportedly committed as many as five serious offences in the course of one night in September.

As is so often the case, Delroy Grant's neighbours found it almost impossible to imagine that the "diamond character" who had been caring tenderly for a wheelchair-bound wife could be suspected of such terrible crimes. And there have already been suggestions that he was questioned by Minstead officers some years ago before being eliminated from the investigation.
 
This morning, after a police operation estimated to have cost £20m, Grant was formally charged with 22 offences, including rape, indecent assault, breaking and entering and burglary.   ·