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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From the time three bodies were found at a house in Oxfordshire to when prime murder suspect Jed Allen was found dead in woodland.
Mostly cloudy overnight, but as low pressure systems feed in as the week goes on an unsettled period can be expected.
The hunt for murder suspect Jed Allen has ended after police found his body two days after discovering his mother, stepdad and sister dead.