Three people have been arrested after a 42-year-old man died in hospital.
It followed an "incident" at a property in Smith Street in Stockton at 22:45 BST on Friday. The man died on Sunday at University Hospital of North Tees.
Three men aged 20, 26 and 28 have been arrested on suspicion of murder, and remain in custody.
Police are appealing for any key workers or members of the public who were travelling in the area at the time to come forward with information.