Police conduct during the period between the arrest of a man for assault and his death in prison three days later is under investigation.
Christopher Shapley, 43, of Aberdare, was found dead in a cell on September 20 after his transfer from South Wales Police custody the day before.
The Independent Police Complaints Commission (IPCC) is looking at police action prior to his transfer to the court and prison service.
The police watchdog will focus on a period from Mr Shapley’s arrest for assault on September 17 when he was taken to Merthyr Tydfil Custody Unit.
The investigation is an automatic referral, under the Police Reform Act, triggered by the contact the force had with him before his death.
Mr Shapley was charged with common assault and threats to kill on September 18 and was remanded in custody before his court hearing on 19 September.
He was then transferred from police custody to HM Prison Cardiff and was discovered dead in his cell on September 20.
Jan Williams, IPCC commissioner for Wales, said: “This is a difficult time for Mr Shapley’s family and friends and they have my every sympathy over their loss. Our investigators have met with Mr Shapley’s family and explained what we will be investigating.
“We will seek to establish what information was available to the police to inform any risk assessments made, how that information was obtained and recorded and whether it was properly shared with other agencies.
“Our investigation will also investigate police actions and decisions, as well as relevant policies and procedures and whether these were followed.”
The Prison Ombudsman will carry out a separate investigation into Mr Shapley’s death.