Investigators are trying to determine why a man targeted a Pennsylvania hospital, taking workers inside the intensive care unit hostage and holding one staff member at gunpoint as her hands were bound by zip ties.

Bearing a pistol, the armed man entered the UPMC Memorial Hospital intensive care unit (ICU) on Saturday and took staff hostage prior to his death, with officials still unsure of the reason for the violent attack. The man, 49, was then killed by police in a shootout as he threatened hostages.

A police officer died and others were injured in what local officials described a hostage crisis involving a man with a gun and zip ties.