The convicted gay serial killer Stephen Port is described as one of the most dangerous individual detectives have ever come across.
A voracious sexual predator - highly devious, self-obsessed, without a shred of remorse.
Over three-and-a-half years he killed four young men - Anthony Walgate, Gabriel Kovari, Daniel Whitworth and Jack Taylor - raped another four, and sexually assaulted two more.
Port admitted nothing, even when shown photos of his victims during police interviews.
The murders, the rapes, the attacks - they all took place at Port's ground-floor, one-bedroom flat at 62 Cooke St.
It's now all boarded up, but it was there he lured his victims, and it was here he drugged them either by spiking their drinks or by injection in order to render them unconscious.
There are 10 distinct similarities that linked the deaths - one was the location of the bodies.
Anthony Walgate's was found outside the block where Port lived in Cooke Street, while the other three were left in or outside the local churchyard, 400 metres away, over the following year.
Barbara Denham found history repeating itself; on a morning stroll she discovered the body of Gabriel Kovari propped up by the local cemetery wall.
And then, three weeks later, she came across the dead figure of Daniel Whitworth in exactly the same place.
In his pocket was a fake suicide note, written by the killer Port. To cover his tracks, the note contained the line "please do not blame the guy I was with last night".
Police accepted it at face value. The local Criminal Investigation Department never probed any links, even the most obvious, until after Port's fourth victim.
Jack Taylor was also found dumped by the cemetery wall, and CCTV footage would later reveal the 25-year-old fork lift truck driver's fatal meeting with Port at Barking Railway Station.
They are tracked walking towards the killer's flat - the last time Jack Taylor was seen alive.
The police put his death down to a self-induced drugs overdose - but his family didn't buy it. Day after day, they pursued their suspicions finding more and more pieces of the jigsaw.
Yet the police remained unconvinced, even though they had already had dealings with their brother's killer, when Port had been prosecuted for perverting the course of justice.
He lied repeatedly in a 999 call alerting police to the body of his first victim, Anthony Walgate, who he had propped up outside his own block of flats.
It was after he was charged and on bail awaiting trial that he went on to kill his second and third victims.
Seventeen officers involved initially in this case have now been placed under investigation by the Independent Police Complaints Commission (IPCC).
The IPCC in a statement said: "It is important we establish whether the police response to the deaths of all four men was thorough and appropriate in the circumstances, including whether discrimination played any part in actions and decisions."
Senior officers have apologised in private to the families for what they term "missed opportunities" during their investigation.
That may not be enough for Jack Taylor's family, who without their own perseverance may never have got justice.
The case of Stephen Port is by no means over - justice may have been delivered, but accountability still waits.
Channel Four
