Island of Fire

A police officer goes undercover in a prison, hoping to determine how the fingerprints of a recently-killed felon could belong to a con who had been executed three months before. While inside, he is tortured for getting involved in internal matters.
His fellow prisoners include Chan, who accidentally killed a card player while trying to raise money for an operation to save his girlfriend's life, Andy Lau Tak Wah, who has himself thrown in jail to exact revenge for his dead brother, Wang, a leader of the prisoners, and Sammo Hung Kam Po, a compassionate but pathetic inmate who frequently escapes to visit his young son.
When Leung kills an especially corrupt guard and is sentenced to a firing squad, he learns that the "executed" convicts are actually used by the warden as hitmen to assassinate untouchable criminals.
(Source: Wikipedia)