A bus passenger was stabbed to death following an altercation with another man in Birmingham on Monday night.
The man, in his thirties, was found injured on the upper deck of the bus in Handsworth.
Police were called to the scene at 10.43pm after a member of the public reported that a passenger had been attacked.
Emergency services tended to the victim at the scene but he died a short time later from his injuries, West Midlands Police said.
He has not yet been formally identified.
Officers are trying to trace the attacker who has been described as a black man, aged about 30 years old. He was wearing a baseball cap and padded jacket and is believed to have left the bus in Rookery Road.
Temporary Superintendent Tom Chisholm, from Force CID, said it was believed that the victim was stabbed following an “altercation” on the upper deck of the outer circle NO 11A bus.
“I am appealing for anyone who was travelling on the bus last night and who has information or anyone who saw the offender after leaving the bus to call police,” he said.
Rookery Road, part of Oxhill Road and Greenhill Road, remained closed on Tuesday morning while forensic enquiries take place. Roads are likely to remain closed for the rest of the day, police said.
Detectives are looking at CCTV and carrying out local enquiries.
Anyone who travelled on the No. 11A bus last night, heading towards the city centre and who may have seen what happened is asked to call police on 101 or contact Crimestoppers anonymously on 0800 555 111.