Detectives investigating the murder of a waiter in 2005 said an unidentified man was "critical" to the inquiry and revealed they have a new forensic lead.
Alexandre Marques's remains were found in Luton on 2 January 2006, more than two months after he was last seen alive in Notting Hill, London on 16 October.
The man was seen using Mr Marques' bank cards between 18 and 24 October 2005.
Det Ch Insp Vicky Tunstall, of the Met Police, said she was confident the man could be recognised from the images.
"Although we're 15 years on, somebody, somewhere must recognise this individual and I'm confident anyone looking at those images, if they know that person, they would recognise them," she said.
Mr Marques, 61, moved to the UK from Lisbon in 1994 and worked at the Arts Club in Piccadilly.
Det Ch Insp Tunstall said the Portuguese national was "openly gay [and] lived a lifestyle centred around socialising".
She said Mr Marques often attended venues such as the Champion pub in Notting Hill Gate, the Quebec bar in Marble Arch and the Leinster pub in Notting Hill.
What happened to Alexandre Marques?
- Mr Marques worked a Saturday night shift on 15 October 2005 and, as usual, took a taxi home arranged by his manager
- The next day a friend visited his flat in Clanricarde Gardens, Notting Hill at 11:00 BST, the last time Mr Marques was seen alive
- Police know he was still alive at 12:11 as he was spoken to by phone by a different friend
- He was reported missing on 24 October after his manager became concerned about his failure to come to work
- Mr Marques's remains were found by members of the public in a grass verge on Woodside Road in Luton, a quiet road near the M1, on 2 January 2006
Since his disappearance, two people have been arrested on suspicion of murder, but were released with no further action.
The case was closed in 2007, but reopened in January 2019 after a "significant piece of information" emerged regarding forensic evidence.
Det Ch Insp Tunstall revealed officers also opened another new line of inquiry in November 2020 related to forensic advancements.
"We are currently working through it," she said.
She said "one of the focal points" was identifying the man in the CCTV images that have been re-released by the force.
He appeared to be wearing tracksuit bottoms with a distinctive white marking on the lower-right leg.
The bank cards were used in the Shepherd's Bush, Cricklewood and Kilburn areas, with the transactions usually from 20:30 to 21:45 between 18 October and 24 October 2005.
"The unidentified male is obviously critical to our investigation," said Det Ch Insp Tunstall.
"This person might hold key information about where Alexandre Marques was on 16 October and what happened to him.
"If that person isn't the person involved in his disappearance then what I'd like to understand is how did that person come into possession of his bank cards."
There remains a £20,000 reward on offer for information leading to a conviction.
As well as people who had contact with Mr Marques in October 2005, detectives also want to speak to those using Woodside Road, Luton in October 2005 - when it is thought his body was left there.
"Any information will be properly treated as highly confidential and I can assure people that their identities can be protected if that is their area of concern," said Det Ch Insp Tunstall.
"Alex's parents are no longer alive, but he does have family still living in Portugal, elderly family members, who would really like to have some resolution found around this and I want to emphasise how committed I am to tracing and identifying the killer."