Detectives have released pictures of a man seen fleeing the scene of the attack on 87-year-old Thomas O’Halloran armed with a knife.
The Met said that officers are keen to identify the man as a “matter of urgency”.
Mr O’Halloran was attacked in Cayton Road, Greenford near the A40 in west London at 4.06pm on Tuesday. No arrests have been made yet in connection with the killing.
Locals told the Standard that Mr O’Halloran was a musician who would often play his accordion to raise money for Ukrainian refugees.