Detectives investigating a fatal attack on a 32-year-old in Hertfordshire are keen to trace a man they believe could have vital information.
The victim, who has yet to be formally identified, sustained injuries at a house in Bowcock Walk, Stevenage, on Tuesday afternoon.
He died shortly after arriving at Lister Hospital.
Police want to speak to a man, described as mixed race and in his late 20s, who was seen in Bowcock Walk.
He is believed to have left the area in a car shortly after 1630 BST on Tuesday.
He has short dark hair and is about 5ft 6in (1.67m) and was wearing black tracksuit bottoms, white trainers and a light-coloured top with black writing across it.
'Deepest sympathy'
A police cordon remains in place at the house while police carry out further investigations.
Det Ch Insp Steve Collin, from the Bedfordshire and Hertfordshire Major Crime Unit, said: "I would ask anyone who knows this man or saw a man fitting his description in the vicinity around the time of the incident to get in touch.
"I would also be keen to speak to anyone who is aware of events leading up to the incident."
Ch Insp Richard Liversidge said: "My deepest sympathy goes out to the victim's family and friends.
"This type of incident is rare in Stevenage. At this time, we believe the man we are seeking is known to the victim."
He added that extra patrols are being carried out in the area.
