A bombing occurred on 140 Broadway's eighth floor on August 20, 1969, injuring 20 people. Police estimated the bomb to be the equivalent of 25 sticks of dynamite, making it among the city's strongest bomb blasts to date. The explosive was placed in a hallway just off the elevators some time during the evening and it exploded at around 10:30 pm. The injured were working on the night shift in the bank's stock bookkeeping department and were working on the other side of the corridor wall. The inside of this wall was lined with floor-to-ceiling automated file units that weighed 3 tons each and which absorbed most of the blast. Still, the blast moved the file units about a foot, blew out all the windows on that side of the building, and opened a hole in the reinforced concrete floor. The bomber, Sam Melville, was convicted of this and seven other 1969 Manhattan bombings and sentenced to 18 years in prison. He was killed by a state sharpshooter during the Attica Prison riot in September 1971. As a result of the bombing, the Marine Midland Company increased security.