Det Ch Insp Stephen Jennings said the evidence was hidden and "anyone who was there knows what happened ".
Mr Lubbock's father says the program will help police work on the case.
Terry Lubbock, who now lives in a care home in Harlow, Essex, said he was determined "to seeStuart get justice ".
" Michael Barrymore is a very, very smart man and he wants to be in the limelight and he wants to come back to television "he said .
"He kept this in the news and I thank him for that.
"I can't imagine Stuart still getting all this attention without Michael Barrymore.
The body of Stuart Lubbock was found in the pool in Roydon, Essex, after a party in which drugs and alcohol were consumed.
He later died at Princess Alexandra Hospital in Harlow, police said.
Tests reveal the 31-year-old man suffered "horrific " sexual assault injuries. An investigation into his death continues.
image source, RORY MULVEY / CHANNEL 4 image caption Terry Lubbock said he solved the mystery of his death. son had "consumed
Terry Lubbock said he hoped the documentary "would open the door a little more ".
"For meoi, her death seems to have been weeks ago, not 19 years ago, "he said.
" As long as I keep breathing I will not stop breathing. fight for him. "
'Geezer ' s dead '
The 90-minute documentary features never-before-seen footage, as well as the 999 call made when Mr. . Lubbock is dead.
Caller said: "A guy drowned in the pool. We took him out.
"There's a party and someone has I just went out and found him. I think the geezer's dead mate.
Mr Jennings, Essex Police Serious Crime Branch, said: 'We made mistakes with regard to the crime scene. Many witnesses said it was a tragic accident, so we believed them at that time.
The scene had been secured "but not to the standard we would expect ", and items - including the pool thermometer - were missing, he added.
image source, CANAL 4 image caption Essex Police admitted mistakes were made in securing the crime scene at Barrymore's home in Roydon
In 2007 Barrymore was arrested in connection with the death , but was subsequently released without charge and retired from public life.
His arrest was ruled unlawful because the officer who made the arrest failed to act. no reasonable grounds to suspect Barrymore, a high court judge has ruled.
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In June, it dropped a claim for compensation against Essex Police, arguing the arrest had damaged his career.
Court of Appeal judges concluded 67-ye Former TV presenter would only be entitled to " nominal "damage .
Last year Barrymore told Piers Morgan in an interview on ITV that he couldn't be more sorry "for the death of Mr. Lubbock but was " 100% innocent ".
Barrymore was approached for comment.
Barrymore: The Body in the Pool will air on Channel 4 at 9:00 p.m. GMT on February 6.
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