A teenager in Luton has died from a stab wound to the heart, a postmortem has revealed.
The 19-year-old boy was found in Hastings Street, Luton, in the early hours of Friday morning. Despite efforts to revive him by police and ambulance services, he died at the scene.
A 43-year-old was arrested at a house just yards from the incident on suspicion of murder and has been bailed.
Detective Chief Inspector Sharn Basra of Bedfordshire Police said officers were looking to speak to four men seen on CCTV heading into an alleyway.
Describing their movements, he said: "It is believed one of the men then returns to the entrance of the alley way and turns right towards The Butcher's public house where he stands and is joined moments later by another member of the group. Both men are then joined by the remaining two group members before they all leave the scene towards Elizabeth Street.
"All the group are described as wearing hooded tops; one is described as black and another is described as a white man with short straight ginger hair which was brushed forward.
"Two other men were also seen on CCTV in the area at around the time of the incident. They are seen to be walking from Hastings Street towards the direction of Windsor Street. These people may be vital witnesses to the incident and I need them to contact the police urgently."
Police also want to speak with a driver and passenger of a car forced to stop when the attacker stood in the middle of the road.
The victim is yet to be named by police.