A man was stabbed in the back as he was sitting on a bench at the junction of St Peter’s Road and Dallow Road, Luton, on April 2.
He was approached by a group of men and stabbed several times, causing back injuries.
The men then left the scene in the direction of Ashburnham Road.
Detective Constable Nick Foster said: “This was an unprovoked attack which could have been a lot worse. I’m urging anyone who may have witnessed the incident to contact us immediately to help identify those responsible.”
The man was taken to hospital with serious but non-life-threatening injuries.
Anyone with information is asked to contact DC Foster on 101, text 07786 200 011, or contact Crimestoppers, anonymously, on 0800 555 111.