Death Warrant (1990) on Netflix

In an abandoned house, detective Louis Burke confronts a maniac called the Sandman. Although the Sandman nearly kills Burke, Burke manages to stop him with a bullet. Sixteen months later, Burke joins a task force put together by the governor to investigate a series of unexplained deaths in the Harrison Penitentiary. While Burke poses as an inmate, attorney Amanda Beckett acts the role of his wife. In the penitentiary, Burke is forced to survive in an environment so dismal and filthy that it makes a public restroom in New York City look like a room in a five star hotel. Burke does succeed in befriending a few of the inmates, including Hawkins and Priest, who help him with the investigation. More inmates are mysteriously murdered. Burke's cell-mate is killed, and prison guard DeGraff puts Burke in solitary confinement, where he's interrogated and beaten. As if that's not enough, the Sandman ends up at Harrison. As it turns out, the prisoners are being murdered for their body organs. Back on the outside, Beckett attends a party given by Vogler, the state's attorney general. Just as she's preparing to tell him about the murders at the prison, Beckett receives a call from her assistant, who identifies Vogler's henchman Keane as the man behind the murders, which also involve Dr. Gottesman, the surgeon who harvests the organs to be sold to people who are in desperate need of them. The assistant's suspicions are confirmed when Vogler tries to kill Beckett. Burke begins an escape from the penitentiary, pursued by the Sandman and hundreds of angry inmates who have been set free and armed with the knowledge that Burke is a cop. Burke and the Sandman have brutal showdown in which Burke tries to get the Sandman out of the way so he can go after Vogler, Keane, and Gottesman.