Port murdered four young men during a 16-month period between 2014 and 2015, luring them to his one-bed flat in Barking before fatally plying them with date-rape drug GHB and then dumping their bodies nearby.
He was initially arrested days after he killed his first victim, but was not charged with murder until after he struck for a fourth time.
The watchdog previously investigated the Met’s probe after the force made a voluntary referral in 2015, and the findings were then shared with the families of the victims and a coroner in 2018.
New inquests into the deaths of Anthony Walgate, Gabriel Kovari, Daniel Whitworth and Jack Taylor concluded in 2021 and found that “investigative failures” by the Met “probably contributed” to the deaths of three of the men.
The inquests also revealed new evidence previously unknown to the IOPC from officers who had been subject to the earlier probe.
IOPC regional director Graham Beesley said: “In our original investigation, we examined the actions of 17 officers. All but one gave no-comment interviews under misconduct caution and chose to provide written responses to the investigators.
“Following analysis of the new information provided at the inquest, we have concluded that the original investigation needed to be wider in scope and, therefore, certain lines of inquiries were not followed. Had this information been known at the time it may have led to different decisions on outcomes.”
Acting Deputy Commissioner Helen Ball said: “The deaths of these four young men is a tragedy and we are deeply sorry there were failings in our police response. Again, I give my own and the Met’s heartfelt apologies.
“The whole of the Met is committed to improving our investigations, our relationships and the trust people have in us to keep them safe.
“Since the deaths of Anthony, Gabriel, Daniel and Jack we have worked hard to ensure the service we provide is better while understanding we have more to do. Learning and recommendations from the Independent Office for Police Conduct, Her Majesty’s Coroner and our LGBT+ Independent Advisory Group of community members have enabled us to make a range of improvements.
“Her Majesty’s Inspectorate of Constabulary and Fire and Rescue Services are with us now carrying out an inspection into how we respond to and investigate death. We look forward to their findings and any recommendations they may have.”
Solicitor Neil Hudgell, speaking on behalf of the victims’ families, said the decision was “the only logical decision open to the IOPC following the weight of evidence heard at the inquests”.
He added: “There remains a big question mark over whether police prejudice played a part in the investigations.
“The inadequate investigations by the Metropolitan Police into the four deaths is one of the most widespread institutional failures in modern history, exacerbated by a woeful lack of remorse, regret or sympathy displayed at the inquests by some of the officers involved.
“Port was jailed for life, but the police have blood on their hands too. It is time for them to be held accountable.”