Entertainer Michael Barrymore will not face charges over the death of Stuart Lubbock at his former home in 2001.
Mr Barrymore had welcomed the re-opening of the police inquiry
He was questioned at Harlow police station in Essex on Monday, along with Justin Merritt and Jonathan Kenny, before all three were released.
The three men were arrested in June and questioned over Mr Lubbock's death.
The Crown Prosecution Service advised that no-one should be charged following a reinvestigation. Essex Police said they will keep the case open.
In 2002 a coroner recorded an open verdict on Mr Lubbock's death.
An inquest heard Mr Lubbock had severe internal injuries and alcohol, ecstasy and cocaine were found in his bloodstream.
A lengthy investigation was carried out by Essex Police, but no-one was charged in connection with Mr Lubbock's death.
Stuart Lubbock's body was found by the side of the swimming pool
The case was reopened in December and Barrymore was arrested alongside the other men.
Chris McCann, complex casework lawyer with Essex CPS, said: "I considered all the evidence and asked Essex Police for further evidence which has now been received.
"If we are ever to consider a prosecution, we must be able to say that Mr Lubbock died as result of the actions of a named person or persons, as shown in the medical explanation for his death.
"I have decided that there is insufficient evidence for a realistic prospect of conviction against the three individuals."
'Big fight ahead'
Terry Lubbock, Stuart's father, said in an interview screened on ITV's Tonight with Trevor McDonald that he could not accept what had happened and he would keep fighting for his son.
"I cannot draw any line under anything that's happened today (Monday)," he said.
"Indeed if I draw any line at all it would be in red, it would be in blood and it would have boxing gloves on because I'm ready for, I'm ready for a big fight ahead now.
"And there's no way that I'm going to lie down and accept anything. I'm going to keep fighting for my son."
Investigating officer Det Supt Gareth Wilson said: "I want to make it very clear this is not the end of the investigation.
"Stuart Lubbock received very serious injuries the night he died and the evidence arising from our current investigations suggest that they occurred at the address in Roydon.
"I am disappointed our latest inquiries have not brought the answers the police and Stuart's family are looking for.
"We remain committed to finding out the truth of what happened that night.
"I am convinced someone knows what happened and I hope their conscience or their obligation to do the right thing will prevail and they will come forward with the information we need."