MIAMI -

Civil rights groups are calling for a federal investigation into the death of a mentally ill prisoner left in a shower so hot that his skin separated from his body.

The American Civil Liberties Union, Amnesty International and other groups sent a letter to the U.S. Department of Justice on June 25.

According to the letter, Darren Rainey was locked in a closet-size shower stall at the Dade Correctional Institution in June 2012 as a form of punishment. He was left unattended for two hours with scalding hot water that later measured as high as 180 degrees. He was found dead.

An investigation by The Miami Herald found Rainey's death was never properly investigated.

A Department of Corrections investigation has been reopened.