The Organ Grinder's Monkey

Lowenkopf and Greeley are called in on a gruesome murder in a psychiatric facility in the Bronx, where the victim has had an internal organ removed and damaged, like other victims of the same killer. Lowenkopf goes undercover in the hospital and learns that a patient in a locked ward is taking credit for the crimes, sending out his spirit to avenge an old injury from a past life. Unwilling to believe his incredible story, but confronted with details only the killer should know, Lowenkopf and Greeley investigate the people around the boasting patient—his doctor, a social worker, and the staff of the hospital. But none of the candidates could possibly have committed the crimes, and Lowenkopf must solve a locked-room puzzle with a madman insisting on his guilt. 

The Organ Grinder’s Monkey is the 3rd book in the Allerton Avenue Precinct Novels, but you may enjoy reading the series in any order.