A murder investigation was launched after a dying man was discovered surrounded by a group of men in High Wycombe.
Thames Valley police said their officers were on patrol in the town, in Buckinghamshire, when they spotted the man, in his 50s, on the ground early Saturday morning.
The force said the group fled the scene on Micklefield Road when a police car arrived.
The man was not breathing when they found him, and officers and paramedics gave him CPR, but he was pronounced dead at the scene.
His closest relatives have been informed. His cause of death has yet to be confirmed.
A man has been arrested on suspicion of murder and is in police custody. There is a large police cordon at the site.
A blue and white forensic tent stood on the sidewalk next to a small roundabout, inside the cordon, Saturday afternoon, PA Media reported.
Several streets were bricked up by police and a forensic officer could be seen working in the area.
Senior Investigating Officer DS Ailsa Kent said: “We urge all men who were at the scene to contact the police as soon as possible as they may have vital information that can assist in our investigation.
“I would appeal to anyone who was in the Micklefield Road and Hicks Farm Rise area in the early hours of this morning, to see or hear something presented.
“If you have any footage, whether it’s a dash cam, CCTV, cell phone, or doorbell camera, keep this footage and contact the police.”
Individuals can contact Thames Valley Police by calling 101 or visiting their website, quoting reference number 59 (7/31).
Alternatively, they can contact Crimestoppers anonymously by calling 0800 555111.