None of the 17 police officers investigated for misconduct over the case of serial killer Stephen Port, who was convicted of the murders of four men, will face disciplinary action, the police watchdog has said.

However, the Independent Office of Police Conduct did identify “systemic failings” within the Metropolitan police, and nine officers will be required to improve their standards.

Port, 44, is serving a whole life sentence after being convicted in 2016 of the murders of Anthony Walgate, 23, Gabriel Kovari, 22, Daniel Whitworth, 21, and Jack Taylor, 25. His trial heard that police had failed to link the deaths.

The IOPC findings emerged as a coroner, sitting at a pre-inquest review at the Old Bailey before next year’s inquests into the four deaths, promised bereaved relatives a “full, fair and fearless” inquiry.

Port met his victims online, invited them to his Barking flat in east London, then drugged and raped them before dumping their bodies in and around a nearby graveyard.

His trial heard that a suicide note, purportedly written by Whitworth, in which he admitted involvement in Kovari’s death, had in fact been written by Port in an attempt to cover up the murders.

Ten Met officers had been served with misconduct notices over the case and a further seven with gross misconduct notices. The 17 ranged in rank from constable to inspector. However, the IOPC findings, which have not yet been published in full, mean none of them will face disciplinary proceedings.

A spokesperson for the IOPC said: “While we agreed none of the officers involved in these investigations may have breached professional standards justifying disciplinary proceedings, we will be making a number of recommendations to the Metropolitan police to address some of the systemic failings our investigation identified.

“We have advised the families of Stephen Port’s victims and the officers involved that the performance of nine officers fell below the standard required. They will now be required to improve their performance … A full report and details of our recommendations will be published at the conclusion of all proceedings.”

Possible police failings during the investigation will be the main focus of the new inquests into the deaths of his four victims.

At the pre-inquest review, Andrew O’Connor QC, counsel for the coroner, told the court: “The main focus of these inquests should be the adequacy of the police investigation into Mr Port.”

Families have questioned why Port was not stopped sooner. Earlier inquests into the deaths of Whitworth, who worked as a chef, and the Slovakian national Kovari, which recorded open verdicts, were subsequently quashed.

The coroner was told it would be unlawful for the new inquests to investigate the conduct of the previous coroner in reaching open verdicts. Families of the victims want the fresh inquests to examine details of what evidence was called at the previous inquiries.

Outlining the proposed scope of the new inquests, Andrew O’Connor QC, counsel for the coroner, said it would examine police knowledge of Port before the death of Walgate, a fashion student, who was his first victim, through to the death of Taylor, a warehouse supervisor, his final victim. It would be necessary for the coroner “to examine the way the police responded to each of the four deaths”, he said.

Port was lawfully entitled to take part in the proceedings as an “interested person”, O’Connor said, adding he was fully aware of the families’ concerns about the killer’s participation. “There is nothing we can do about his entitlement,” he said.

It was not known if Port wanted to participate, but if he did it was suggested he could hear evidence via video link from prison, and any questions he had could be put to the court through the coroner’s counsel.

The full scope of the inquests is yet to be determined. The counsel for the bereaved argued that it should be allowed to examine the actions of the coroner at the original inquest into the deaths of Kovari and Whitworth. O’Connor said Judge Sarah Munro QC, sitting as an assistant coroner, had no power to do so. He added that witnesses, and police officers who took part, could be asked what they did before those inquests, and “what they did or did not do after those inquests”.

It is yet to be decided if the inquests, which are likely to be held in early 2020, will be heard before a jury. Another pre-inquest review will be held in November.

John Pape, Kovari’s former flatmate, who had raised concerns with the Met during the police investigation into the deaths, said the IOPC announcement made his “blood boil”.

He told the BBC it “contrasted with the basic facts of that disturbingly incompetent initial investigation”, adding: “Given the open goal they were given, it makes me wonder what the point of the IOPC is.”

Pape said he was “not clamouring for individual officers to be harshly punished” but was concerned about the consequences for the LGBT community and their families, of “institutionalised incompetence and prejudice within an unaccountable police force”.