Police are offering a £15,000 reward over the murder of a teenager stabbed to death in a park.
Jamil Palmer, 18, was found slumped in the road near Evans Grove in Feltham, Hounslow, west London, with a stab wound on May 6.
Detectives have also released a photograph of a Somalian man who had "an altercation" with Mr Palmer earlier that day.
Officers want to speak with Mahamed Barre, 18, who received a head injury in the disagreement and may have required medical treatment, Scotland Yard said.
Detective Chief Inspector Noel McHugh, of the homicide and major crime command, said: "I am seeking help from the local community to help locate Mahamed Barre. I would ask anyone who knows of his whereabouts, or has any information that could assist us, to come forward.
He added: "I also appeal directly to Mahamed Barre to present himself at a police station so this matter can be dealt with."
Four teenagers - two 16-year-olds and two 15-year-olds - have previously been charged with Mr Palmer's murder.
The £15,000 reward is being offered for information leading to the arrest and prosecution of those responsible for the murder.
Anyone with information should call police on 020 8785 8099 or Crimestoppers on 0800 555 111.