Caught on tape: CCTV filmed horrific moment of woman's crossbow killing

More reports and background on Stephen Griffiths

He set the videotape to fast-forward and searched through the recordings, hoping to spot any vandalism or petty crime that might have occurred since he last sat there, the Friday before.

Instead, he witnessed the horrifying final moments of a desperate woman's tragic life, the third of three killings by a PhD student who would later describe himself as the Crossbow Cannibal.

The footage showed a man and a woman entering the building in the early hours of Saturday, May 22, heading upstairs and going into Flat 33 on the third floor.

Minutes later, the woman ran back into the corridor, only for the man to give chase, grab her, overpower her and drag her back towards the front door of the flat.

The man picked up a crossbow, pointed it at the woman's body and fired.

After dragging the woman's lifeless body back into the flat, he returned to the corridor and, still holding the crossbow, approached the camera lens, raising one finger in contempt.

The man was Stephen Griffiths, the troublesome resident of Flat 33 for the past 13 years, whom Mr Gee had been warned by his bosses not to approach because his anti-social behaviour often ended in violence.

The woman was Suzanne Blamires, a prostitute who had been reported missing by her boyfriend. She was never seen alive again.

Discovering the footage was the pivotal moment in a case which had frustrated West Yorkshire Police for 11 months – and it confirmed detectives' fears that what once had been a painstaking missing persons investigation was in fact a triple murder inquiry.

It also revealed that the man responsible for the killings had not been on the police's initial list of suspects, despite having a criminal record which included convictions for violence.

The case began in June 2009 when Susan Rushworth was reported missing. A sex worker with epilepsy and an addiction to heroin, police classed her as a "high-risk" individual.

Several drug addicts had died in Bradford in the previous few weeks – a trend blamed on a "rogue" batch of heroin doing the rounds – and, within 25 hours of her disappearance being reported, the case was handed to West Yorkshire's elite homicide and major enquiry team (HMET) for a senior detective and a full investigation team to pursue.

Detectives organised a series of high-profile appeals for information but, even after arresting some of Ms Rushworth's associates on the Bradford drugs scene, they found no evidence to suggest that she had been the victim of a crime.

Months passed, and no significant leads came to light – even after another prostitute, Shelley Armitage, was reported missing on April 28 this year.

Ms Armitage was last seen on the evening of April 26, leaving her flat in the Allerton area of Bradford, going out for some food and then walking to Bradford's red light district.

Like Ms Rushworth, Ms Armitage had issues with drugs and the two cases had several common features, but police decided to keep the inquiries separate.

"Working girls don't just disappear, as a rule, unless they have come to some harm," said acting Detective Chief Superintendent Andy Brennan, acting head of HMET.

"The incident rooms were linked, but we kept the two inquiry teams going because we didn't want to miss anything. We wanted separate teams on it so that every piece of evidence was referenced in its own right."

Detectives began compiling a list of suspects, starting with known offenders who lived near Bradford's red light district and had previous convictions for attacking prostitutes or kerb-crawling.

After eliminating those suspects from their enquiries, they intended to widen their search to include other criminals who had been convicted or suspected of violence against women. They also put in place a "trigger plan" that would commit more officers to the investigations if more sex workers were reported missing.

The plan came into effect when Ms Blamires disappeared.

Mr Brennan said: "Between Shelley's disappearance and Suzanne's disappearance, we had about a dozen sex workers go missing because of the lifestyle they led and the tensions they had with their families, but they all turned up.

"When Suzanne went missing, we approached it in the same way and a detective superintendent on the case within two hours.

"Only this time we couldn't find her."

Ms Blamires's disappearance remained a mystery for only two days. After viewing the footage, Mr Gee informed his manager, who called the police.

"I think we would have been knocking on Griffiths's door," Mr Brennan said, "but he wasn't one of the first people we approached.

"First, we would see if any local residents had convictions for attacks against sex workers, and then we would see if any had had any dealings with sex workers.

"There was no intelligence linking Griffiths to sex workers but, eventually, I think we would have found him a long way into our inquiry because of his previous convictions."