Abuse of authority

The story

A police officer tries to discover the murderer of his brother, who was a pianist and a morphine. As a member of the Drug Enforcement Department, he tries to identify the head of a drug dealer gang. His unorthodox way of acting upsets his superiors, even though they allow him to continue his investigations. When the gang discovers that he is a police officer, he makes him a drug addict, but he manages to detoxify and eventually capture the gang's brain.