Bucks County Coroner Joseph Campbell said Sunday that the gunman - 58-year-old Mark McCarpy of Levittown died of a self-inflicted gunshot wound to the chest.
The incident began around 7:30 p.m. Saturday along Commerce Boulevard in Fairless Hills.
Sources tell Action News that he went into the sporting section and asked to see a shotgun and ammunition.
The store clerk complied and McCarpy allegedly pulled out a handgun and told the clerk to undo the gun lock on the shotgun.
Witnesses say McCarpy then took the shotgun and ammunition and ran to the bathroom, barricading himself inside.
"It's quite scary, just looking at it, how serious things can go wrong so quickly," said Nicole Didonato.
Ted Jusinksi, who was in the store with his son, says they thought McCarpy was one of the employees.
"He walked only a foot behind him. In retrospect I'm thinking he could have grabbed him easily and used him as a hostage in anyway if he needed to. The afterthought of that is horrifying," said Jusinksi
Authorities quickly evacuated people from that store and surrounding others.
Police were never able to make contact with McCarpy. A robot was later sent in but it was discovered that he was already dead.
Falls Township Police say the suspect had a history with law enforcement including a 2002 standoff in Middletown. In 2010, he was committed into a mental institution.
The Associated Press contributed to this report.