Though Keenan’s British parents had settled in New York before he was born, his mother traveled to England to give birth to him, and then brought him home to Brooklyn. In 1941, after high school, he joined the New York Police Dept., but his career was interrupted by World War II: Keenan was in both the Battle of the Bulge and the D-Day invasion of Normandy as a member of the U.S. Army’s Fourth Infantry Division’s Counter Intelligence Corps. After he was discharged as a lieutenant, Keenan returned to the NYPD, and rose in rank until he was promoted to Chief of Detectives. In 1977 he announced that he would allow female detectives to serve in the Homicide Unit not because of the “trend of women’s lib,” but because of women’s “tenacity and inquisitiveness — qualities that are especially important in homicide work.”
During that time, Keenan was in charge of a major investigation: starting in summer 1976, a string of murders were committed and investigators noticed a pattern: the victims were often couples in a car who were parked alone, and the weapon used was a .44 caliber revolver. The perpetrator was dubbed the “.44 Caliber Killer” but later, after the serial killer taunted police in a letter left with his latest victims, he was re-dubbed by the name he used there: “Son of Sam”. With the city gripped by panic, Keenan assigned more and more resources to the case. At the height of the manhunt, 75 detectives and 225 officers were actively working to find the murderer. They finally caught a break: after a couple was shot on July 31, 1977, a woman called police to provide a tip, that she had seen a suspicious man run near her holding a “dark object” in his hand. He had looked at her intently, and so she ran — and shortly after heard shots fired behind her. He had come, she said, from a car that she noticed a patrol officer had cited for a parking violation. One of several ticketed vehicles in the area was registered to David Berkowitz of Yonkers, a 24-year-old letter sorter for the U.S. Postal Service. At about the same time, Yonkers Police notified NYPD of their suspicion that Berkowitz was the Son of Sam. Berkowitz was arrested and taken to Chief Detective Keenan.
Upon seeing Keenan, Berkowitz said, “I know you. You’re Detective Chief Keenan.” Keenan replied, “Yeah? Who are you?” Berkowitz answered, “I’m the Son of Sam.” With that rapport established, Keenan himself obtained a full confession from the killer. Berkowitz pleaded guilty and was sentenced to 25 years to life, becoming eligible for parole in 2002. He has been denied release after 19 parole hearings; his next such hearing is in May 2020. After more than 30 years with NYPD, Chief Keenan retired several months after the case was solved. He died in a Long Island hospital on September 19, from congestive heart failure, at 99.