Serial killer Stephen Port was identified as a sex assault suspect on the day his first victim died, an inquest has heard.
Port was noted as a "significant witness" after the body of Anthony Walgate, 23, was discovered slumped against a wall outside Port's flat in Cooke Street, Barking, east London.
Officers arrived on the scene following an anonymous 999 call at 4.05am on 19 June, 2014, with Port later identified as the caller.
The first officer to attend the scene following the call said he was unaware of the serious allegation against 6ft 5in Port, which dated back to 2012. The allegation has been noted by the borough commander that day.
Over the next 16 months, Port went on to kill three more young gay men, Gabriel Kovari, 22, Daniel Whitworth, 21, and 25-year-old Jack Taylor, with overdoses of the drug GHB before he was stopped.
The inquest into the young men's deaths is examining whether police mistakes prevented Port from being stopped before he could kill some of his victims.
Inspector Gary Learmonth gave evidence on Friday, saying he arrived at the scene at 4.30am and stayed for four-and-a-half hours.
Mr Walgate had a "fat lip" and a "possible footprint" on his torso so a "critical incident" was declared, jurors heard.
"We had a young man who was deceased in a public place. It was not clear at that stage how this had occurred," Mr Learmonth said.
He assessed the death as "potentially suspicious".
By 5.16am, records showed Port had been identified as the anonymous caller and his last known address was 62 Cooke Street.
Andrew O'Connor QC, counsel for the coroner, said: "You had his name and you had his address pretty much where you were standing."
The witness told jurors that officers were keen to speak to Port, but his number went to voicemail and officers repeatedly knocked on the door of his flat to no response.
An officer eventually took a statement from Port at 7.50am.
The inquest was shown a note by the borough commander, Chief Superintendent Andy Ewing, the same day stating "caller previous sex assault".
Mr Learmonth said he did not recall being told of the allegation against Port.
The allegation was printed off the Police National Computer (PNC) a week later.
Mr O'Connor said: "If someone within the police service had found that information that morning would you expect to be told about it?"
Mr Learmonth said: "Yes, there is some overlap but yes, potentially I would be one of those persons that would have been updated."
The PNC report shown to jurors outlined an allegation Port had raped a man at his flat on New Year's Eve in 2012.
Mr O'Connor said: "If it is right, that information was discovered that morning, that was a significant piece of information about the person who had called 999?"
The officer said: "Yes, I agree."
A crime report also shown to jurors revealed the complainant had gone further and described several different occasions of non-consensual sex in which he was plied with drugs and alcohol.
But no further action was taken after the complainant said he did not support a prosecution, jurors heard.
Port was found guilty of all four murders and handed a whole life sentence after a trial at the Old Bailey in 2016.
The hearing has been adjourned until Monday morning.