The police watchdog is investigating the death of a man who had been detained by officers.
Cambridgeshire police were called after a man, 42, was reported to be apparently unwell in Oundle Road, Peterborough, on 30 July.
Officers detained him but his condition deteriorated and he died at the scene.
The force has referred itself to the Independent Office for Police Conduct (IOPC), which is investigating.
A police spokeswoman said: "Police were called at 16:30 BST on 30 July to reports of concern for the welfare of a man who had become unwell and was walking into oncoming traffic in Oundle Road, Peterborough.
"Officers attended and detained the man before commencing CPR. However, despite best efforts, the man, aged in his 40s, died at the scene."
"Due to officers being in contact with the man before he died, a referral was made to the Independent Office for Police Conduct who are now investigating the circumstances.
"It would be inappropriate to comment any further at this stage."
The IOPC said it had spoken with officers and viewed bodycam footage, but is asking for anyone who witnessed the interaction to come forward.
Regional director Sarah Green said: "Our thoughts are with the man's family and friends, and all those affected by this incident.
"We are in the process of gathering as much evidence as possible in order to establish and examine the circumstances of what happened."