Thames Valley Police is appealing for a specific witness following an assault in Milton Keynes.
At around 11pm on Saturday 25 July, a man was talking to a friend on North Ninth Street when he was approached by a group of four men.
The men started to punch and kick him.
A member of the public called at the group for them to stop and the group ran off in the direction of the shopping centre.
The victim sustained cuts and bruising to his head.
One of the offenders is described as a large white man, around 30 years-old and approximately 5ft 10ins tall. He had short dark hair and was wearing a dark blue tracksuit with dark blue trainers.
A second member of the group is described as a stocky white man, between 30 to 40-years-old and approximate 5ft 10ins tall. He had slicked back dark hair and was wearing a light coloured tracksuit.
Investigating officer PC Antony Hurd, based at Milton Keynes police station, said: “I am appealing to the member of the public who shouted at the group to get in contact with us. I believe that you can provide us with information that could prove vital in bringing these offenders to justice."
"I would also like to hear from anyone who may have seen or heard anything or have any information that could assist this investigation."
"You can contact us using our online form or by calling 101, quoting reference number 43200232532. Alternatively, you can contact the independent charity Crimestoppers anonymously via their website or on 0800 555 111.”