Detective chief superintendent Steve Worron said officers are "particularly seeking a murder weapon" in their investigation into the killing of a woman in Colchester, Essex last week.
He said they are looking for a clean-shaven, tanned man in his late teens, with thick "mop-like" dark hair.
Detectives said the man was wearing a "distinctive" beige jacket.
More top news
The home of a Premier League footballer has been burgled while he was away with his club for a match
A giant 'death ray' is being offered free to a good home on Gumtree.
The British Government has urged the world football governing body FIFA to publish the Garcia report into World Cup bidding in full