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.
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There will be blustery showers across northern parts overnight with showery rain and sleet across the south.