“Crime scene mistakes” were made in the investigation into the rape and murder of a man at Michael Barrymore’s home, Essex Police have said.
The admission comes in a Channel 4 documentary 19 years after Stuart Lubbock’s body was found in the TV presenter’s pool following a party.
Det Ch Insp Stephen Jennings said evidence was hidden and “someone that was there knows what happened”.
Mr Lubbock’s father says the programme will help police working on the case.
Terry Lubbock, who now lives in a care home in Harlow, Essex, said he was determined “to see Stuart get justice”.
“Michael Barrymore is a very, very clever man and he wants to be in the limelight and he wants to be back on television,” he said.
“He’s kept this in the news and I thank him for it.
“I cannot imagine Stuart would still be getting all this attention without Michael Barrymore.”
Stuart Lubbock’s body was found in the pool in Roydon, Essex, after a party in which drugs and alcohol were taken.
Tests revealed the 31-year-old suffered “horrific” sexual assault injuries. An investigation into his death continues.
Terry Lubbock said he hoped the documentary would “push the door open a bit more”.
“To me his death seems like it was weeks ago, not 19 years ago,” he said.
“As long as I keep breathing I won’t stop fighting for him.”
The 90-minute documentary includes previously unseen images, as well as the 999 call made when Mr Lubbock died.
The caller said: “A fella has drowned in the pool. We have got him out.
“There’s a party going on and someone has just gone out and found him. I think the geezer’s dead mate.”
Mr Jennings, from Essex Police’s serious crime directorate, said: “We did make mistakes in terms of the crime scene. A lot of witnesses said it was a tragic accident so we believed them at that point.”
The scene had been secured “but not to the standard we would expect”, and items – including the pool thermometer – had gone missing, he added.
In 2007 Barrymore was arrested in connection with the death but was later released without charge, and withdrew from public life.
His arrest was found to be unlawful because the arresting officer did not have reasonable grounds to suspect Barrymore, a high court judge ruled.
In June he dropped a compensation claim against Essex Police, arguing the arrest had damaged his career.
Court of Appeal judges concluded the 67-year-old TV presenter would be entitled to only “nominal” damages.
Last year, Barrymore told Piers Morgan in an interview on ITV he “couldn’t be more sorry” for the death of Mr Lubbock but was “100% innocent”.
Barrymore has been approached for comment.
Barrymore: The Body in the Pool airs on Channel 4 at 21:00 GMT on 6 February.