The detective in charge of the investigation into serial killer Stephen Port’s first victim has admitted making “significant mistakes” in the case, including not properly looking into the drug-rape predator’s history.

Detective Sergeant Martin O’Donnell told inquest jurors how he did not share intelligence with colleagues about a previous allegation that Port plied a young man with drugs before raping him, nor did he instruct a search on the police national database about Port.

The latter meant Mr O’Donnell was unaware British Transport Police files showed Port was found at Barking Station, a short walk from his flat in east London, with another man who was under the influence of drugs, the same month Port plied his first victim, 23-year-old Anthony Walgate, with fatal doses of the substance GHB.

Giving evidence at the inquest into the deaths of Port’s four victims, Mr O’Donnell, the officer in charge of the investigation for the first few months, said: “It’s just a huge failure not to have obtained that (information).”

Port had initially been arrested on suspicion of raping a man in December 2012, but the case was dropped when the alleged victim said he did not support a prosecution, despite again stating Port “forced” him to have sex after giving him drugs.

But Mr O’Donnell did not update the Crime Reporting Information System (CRIS), which logs progress in an investigation for colleagues to see.

He told the hearing at Barking Town Hall: “It feels like a fairly significant mistake of mine not to include it in that document.

“It’s a terrible mistake that I did not put it in there.”

The inquest previously heard Port repeatedly changed his account over Mr Walgate’s death – initially telling emergency services he chanced upon the aspiring fashion designer slumped by the communal entrance to his house on June 19 2014, to later admitting he agreed to meet the young escort for sex.

Andrew O’Connor QC, counsel to the inquest, said: “Stephen Port lied to police about his dealings with Anthony, there were suspicions his death was caused by drugs, and you have a detailed account that he (Port) forced drugs on him (the rape complainant) on more than one occasion.”

Mr O’Donnell replied: “Yes, you’re absolutely right, that should have gone on that report.”

The detective’s evidence echoed the testimonies of other officers that his team had been over-worked at the time.

He said: “There was enormous pressure in the office at the time.

“We discussed what we were doing at the time as spinning plates – you would rush to one plate that seemed to be crashing down, then another plate that seemed to be crashing down. It was easy to miss things.”

His colleagues, Detective Constable Nainesh Desai and Detective Constable David Parish, previously told the inquest how they made mistakes over the deaths.

Mr Desai said he failed to link the first two deaths – despite both victims being young, gay men, found a short distance from Port’s flat, and who were later found to have been drugged – while Mr Parish did not send the predator’s laptop for analysis in the days after he first struck.

Jurors are being asked to assess whether the victims’ lives could have been saved had police acted differently.

Mr Walgate, Gabriel Kovari, 22, Daniel Whitworth, 21, and Jack Taylor, 25, were all found dead near Port’s flat during a 16-month period between June 2014 and September 2015.

Port, now 46, was found guilty at the Old Bailey in 2016 of the four murders and sentenced to a whole life order.

The inquest continues.