On April 22, 1922 at 10:30 am, Officers Michael O'Connor and Bernard Mengel were shot and killed while responding to a robbery on South Broadway. The two officers and Officer Held were guarding money at the South Side Trust Company. A man ran in and notified the officers the office of Morris Packing Company was being robbed across the street. As the three officers exited the trust company they engaged the suspects, Charles Merrill and Hugh Pinkley, and a shootout erupted. Officer O'Connor fired one shot through the door at the robbers. The robbers exited the doorway at Morris Packing Company and shot Officer O'Connor striking him in the chest and head. Officer Mengel also sustained a fatal gunshot wound to the head as he closed with the robbery suspects. Officer Held exchanged gunfire with the suspects and sustained a gunshot wound to his right shoulder. The suspects escaped with $100.

After tracking the suspect vehicle later that day to a residence at 1329 N. Vandeventer, police detectives arrested Merrell and Pinkley and a third suspect, Robert Manley. Manly confessed to being the getaway driver implicating Merrell and Pinkley in the robbery and murder. Merrell and Pinkley were hanged at the St. Louis City Jail on July 18, 1924 at 4:05 pm. Manly's murder charge was dismissed by the circuit attorney.

Officer Mengel was survived by his wife, Lillie. Interred: Mt. Olive Cemetery.

Officer O'Connor, born in Ireland, was survived by his wife. Interred: Calvary Cemetery.