On March 9, 1977, Mack Wesley Cantrell, a 46-year-old security guard, was on duty at the District Building in Washington, D.C., when Hanafi gunmen led by Hamaas Abdul Khaalis mounted a coordinated daytime siege of three buildings. The attackers took hostages and in the initial violence Cantrell was hit by a shotgun blast that entered under his eye, tracked around his skull beneath the skin, and exited at the back of his head. Reporter Maurice Williams was killed in the same burst of violence and City Council member Marion Barry was wounded.

After 39 tense hours the standoff ended with the surrender of twelve gunmen, who were later tried and convicted. Cantrell survived the head wound and recovered enough to return to work. On his first day back he suffered a massive coronary thrombosis and was taken to Washington Hospital Center, where he died on Monday, July 4, 1977. The heart attack was reported as the immediate cause of death and was widely believed to be a direct consequence of the earlier trauma.