An MI6 spy found dead in a padlocked holdall in his central London flat had accessed bondage websites several times, police have revealed.
Gareth Williams, 31, from Holyhead on Anglesey, had also visited a drag show and owned £15,000 worth of women's designer clothing, detectives said.
Mr Williams' naked body was found at his Pimlico flat in August.
Police believe other people helped the MI6 codebreaker to get into the holdall and want to speak to them.
Officers have released e-fit images of a couple who they said visited Mr Williams' Alderney Street home in June or July.
The Met said disclosure of "embarrassing, hurtful and distressing" details was necessary to get some information as detectives believe "someone else was in the flat".
Det Ch Insp Jackie Sebire said: "We know he was intensely private, and however difficult this might be for someone who has had any interaction with Gareth, it would really help us if they came forward so we know if that side of his life had any relevance to his death.
"If he was alive, he got into it voluntarily or, if not, he was unconscious and placed in the bag," she added.
Police revealed Mr Williams viewed websites showing people bound and tied, which included do-it-yourself guides.
The two e-fit images issued by police show a casually-dressed couple of Mediterranean appearance, thought to be in their 20s, who were buzzed through the communal entrance of his home by another resident in late June or July.
The GCHQ code-breaker, who had been on secondment to the spy agency, was found dead by police after concerns were raised for his welfare.
No evidence of drugs, alcohol or poisons were found during a series of tests conducted by toxicologists.
Det Ch Insp Sebire revealed police had forensic evidence that other people were in the flat, whom they have not been able to trace.
She added that an expert, brought in to examine the red holdall in which Mr Williams was found, concluded he could not have locked it.
The keys were found inside the bag.
She said experts had said the temperature inside the bag would have risen to 30C (80F) within three minutes and he would have suffocated inside half-an-hour.
Fashion design courses
The detective added Mr Williams probably died in the early hours of 16 August, a week before he was found.
He had a collection of six boxes of unworn designer clothing in a wardrobe, she said.
Mrs Sebire said Mr Williams attended two fashion design courses at Central St Martins College in 2009 and 2010, and said the items could have been related to those diploma courses.
The detective said although a witness had reported seeing Mr Williams in a gay bar, police do not know for certain he was gay.
She said Mr Williams occasionally spent between 30 minutes and an hour on bondage sites, but added there was no evidence that he was "obsessed" with bondage and no other pornography was found.
Police also revealed that the spy visited a drag cabaret in east London four days before his death and held tickets to two more.
Det Ch Supt Hamish Campbell said investigators were sure someone else involved with the bondage or gay scene had "linked in" with Mr Williams but police "cannot find that trace".
The death remains suspicious and unexplained and no conclusive cause has been found.
An inquest will be held at Westminster Coroner's Court on 15 February.
Police have asked anyone with information to call the incident room in Hendon on 020 8358 0200. If the caller wants to remain anonymous, he or she could contact Crimestoppers on 0800 555 111.