The man, whose name was not reported, entered the Dick's Sporting Goods store in Falls, Pa., at approximately 7 p.m. Saturday and asked to see a 12-gauge shotgun at the firearms display, police told Phillyburbs.com.
The clerk refused to take off a lock on the gun until the man pulled out a revolver and pointed it at the clerk. The man told the clerk to leave and the store was evacuated, the website said.
Police arrived on the scene about 10 minutes after the incident began and had a brief confrontation with the man before he retreated to the bathroom area of the store, the news website reported.
After about three hours of no contact with the man, police sent in a robot that found him dead in one of the bathrooms.
Police said there were no notes left behind to indicate a motive for the standoff and suicide.
The man had previous contact with police, including a standoff in 2002 in Middletown, Pa. He was involuntarily committed in 2010 for mental health treatment, Phillyburbs.com reported.
Jessica Simpson shares three-way kiss with friends in photo
Susan Sarandon 'very excited' about daughter's pregnancy