A man arrested in March on suspicion of the indecent assault and murder of Stuart Lubbock at the home of entertainer Michael Barrymore in 2001 has been released without charge.
Essex Police said there was insufficient evidence for a “realistic chance of a successful prosecution” so the man had been released without further action.
Detective Chief Inspector Stephen Jennings said the news was a “huge personal disappointment” to all the detectives involved in the case.
“We have explored all possible lines of enquiry and sometimes, regrettably, the evidence is not yet there to issue charges. I know that this may be of little comfort to Stuart’s father and his family,” he said.
“At every stage, it is the Lubbock family and our search for justice for them that dominates our thoughts and our actions. We have tried our best. We will continue to try our best.
“For the last 20 years, as we have continually stated, two things have remained consistent. One is the commitment of Essex Police to deliver justice for Stuart and his father Terry.
“The second is that we believe of those present on the night Stuart died, someone at the house was responsible and someone knows what happened.”
He added the force has “never given up on this case” and all they want is to “deliver justice for Mr Lubbock and his family”.
Mr Lubbock was attending a party at Barrymore’s luxury home in Roydon with eight other people on March 31 2001 when he died.
A post-mortem examination showed the 31-year-old had suffered severe internal injuries which suggested he had been sexually assaulted.
Alcohol, ecstasy and cocaine were found in his bloodstream.
The coroner recorded an open verdict.
A friend of Terry Lubbock, Harry Cichy, said Stuart’s father has campaigned for justice for his son for years and is now seriously ill.
Mr Cichy told PA: “I’ve spoken to Terry, and he wants the police to review the decision.”
No-one has ever been charged with any offence in relation to Mr Lubbock’s death.
Barrymore, now 69, was arrested in 2007 but never charged with any offence.
He subsequently sued Essex Police, and claimed a wrongful arrest had cost him about £2.5 million in lost earnings, but Court of Appeal judges concluded he should receive nominal damages.
A spokesperson for Barrymore declined to comment.