He has been named locally as Nigel Leigh, of Fossa, Killarney, and his death has been described as tragic and sudden.
The Garda Síochána Ombudsman Commission (GSOC) is investigating the case as he had been arrested for public-order offences near his home and brought to Killarney Garda Station at around 8pm on Thursday.
He was transferred by ambulance to Kerry General Hospital in Tralee about 30 minutes later. A spokesperson for the HSE said Mr Leigh discharged himself against medical advice.
The body was discovered near the carwash area of Kelliher’s garage, Rathass, Tralee, on the hospital perimeter, just before 7am yesterday.
As he had been in contact with gardaí prior to his death, the incident was referred to the GSOC for independent investigation.
GSOC investigators are appealing for anyone who may have encountered him in the early hours of yesterday, or anyone with information which may assist the investigation, to contact them on 1890 600800.
Meanwhile, the issue of deaths of people in custody, or shortly after release, was raised at the annual conference of the Association of Garda Sergeants and Inspectors, this week.
Association president Tim Galvin said they had been in contact with the Department of Justice about changing the law to give gardaí the legal power to detain people arrested under the Public Order Act for their own safety.
He told Justice Minister Frances Fitzgerald the association had concerns that GSOC ended up carrying out investigations in relation to deaths in custody or deaths shortly after release.
Ms Fitzgerald said she had asked her officials to examine these issues “as a matter of emergency”.