That easy carefree time came to an end on June 13th 1974 around 9:30 Pm when the Guard watching the desk gets a call telling him he had 20 minutes to evacuate the building there was a bomb and several minutes latter there was a massive explosion on the 29th floor luckily no one was hurt and emergency officials who had been checking out the building had just cleared the area before it went off .
The Gulf Building was targeted supposedly by The Weather Underground because the famous Gulf Oil Company was headquartered there and the Weather Underground held them responsible for supposed deaths they caused to native Africans during there oil explorations.
The building from that day on was sealed off no more of the public just walking in and the observation deck was closed forever .
The Pittsburgh Police and FBI would investigate along with Allegheny county Detectives but no suspects where developed or arrests ever made . Of course back then Closed Circuit cameras where still in there infancy and few where deployed and most did not record. To my knowledge the Gulf building did not have them. I suspectsome one posing as a cleaner or contractor planted the explosives and since no one checked in back in those days the Gulf Building was an easy open target.