Police investigating the murder of a man in Welwyn Garden City say they believe there was a "serious altercation" involving four men shortly before the victim was stabbed.
A 23-year-old man from London was found on Ludwick Way late on Thursday night. He died at the scene.
Officers think there was a fight on Ethelred Close moments before.
A 19-year-old man who was arrested in connection with the incident is still being questioned.
“Did you see anything suspicious or out of the ordinary on Thursday evening? We are also trying to identify a 4x4 car that was seen to leave the area shortly after the incident," Detective Chief Inspector Jerome Kent said.
“I appeal to anyone who might have witnessed something or who knows anything at all about the incident to get in touch with us as soon as possible.”