The Metropolitan Police have made payments to families of three gay men who were killed by Stephen Port over investigatory “failings”.
The Independent Office for Police Conduct (IOPC) is reinvestigating the Met over its initial handling of their cases.
The watchdog said there is evidence that the original probe into the conduct of officers was “materially flawed”.
It added that “new information” had come forward at inquests last year into the deaths of the four men.
A spokesperson for the Met said in a statement: “The Metropolitan Police Service has settled civil claims from the families of Anthony Walgate and Gabriel Kovari as well as the partner of Daniel Whitworth.
“We have previously apologised to the families for the police failings in this matter and understand the impact these have had and the distress caused. We apologise again now.
“Our thoughts and sympathies are with the families as always.”
In January, a coroner’s report on the deaths of Port’s victims identified a “large number of very serious and very basic investigative failings” by police.
This included a “lack of professional curiosity” about the cases.
The report, by Sarah Munro QC, also expressed concern over how deaths are classified as “unexplained” rather than suspicious.
Senior police officials said they would reform the national approach to investigating unexplained deaths so that they would be more clearly categorised and pursued.
An inquest jury found that officers in Barking missed repeated opportunities to catch Port after he plied his first victim, Mr Walgate, with a fatal dose of the date-rape drug GHB and dumped his body.
Port struck three more times before he was caught, killing each victim in near-identical circumstances, with police failing to link him to the deaths despite detective work carried out by the victims’ family and friends that would lead to the culprit.
Officers had denied accusations of prejudice and homophobia, blaming mistakes on being understaffed and lacking resources.