A murder investigation was opened after a dying man was discovered surrounded by a group of men in High Wycombe.
Thames Valley Police said his officers were patrolling the town, Buckinghamshire, when they saw the man, in his 50s, on the ground in the early hours of Saturday.
The force said the group fled the scene of Micklefield Road when a police car arrived.
The man was not breathing when he was found, and police and paramedics administered CPR to him, but he was pronounced dead at the scene.
His relatives have been informed. The cause of his death has not yet been confirmed.
A man suspected of murder has been arrested and taken into police custody. A large police cordon is in place on the scene.
A blue and white forensic tent had been set up on the sidewalk near a small roundabout, inside the cordon, on Saturday afternoon, PA Media reported.
Several streets were cordoned off by police and a medical examiner was working in the area.
DS Senior Investigating Officer Ailsa Kent said: ‘We urge all men at the scene to contact the police as soon as possible as they may have vital information that can aid our investigation.
“I would appeal to anyone in the Micklefield Road and Hicks Farm Rise area in the early hours of this morning who saw or heard something coming.
“If you have any footage, whether it’s an edge camera, CCTV, cell phone, or a doorbell camera, please keep those footage and contact the police. “
People can contact Thames Valley Police by calling 101 or visiting their website, citing reference number 59 (31/7).
Alternatively, they can contact Crimestoppers anonymously by calling 0800 555 111.