Klein Michael Thaxton, a 22-year-old military veteran, allegedly held the hostage on the 16th floor of Three Gateway Center, in an ordeal which lasted around six hours from 8:00 am (1200 GMT).
Klein gave himself up without incident and was arrested, said FBI spokeswoman Kelly Kochamba, who earlier had identified the hostage as a woman. She could not confirm which weapon or weapons Klein held during the incident.
Earlier, Pittsburgh Police Chief Nate Harper told reporters at the scene that Klein has a criminal record but was “not irrational.” Harper also indicated there were two hostages.
The suspect’s Facebook page indicates he was “obviously distressed,” Kochamba said, adding that his motives were unclear. It was also not clear whether he had any connection to the business where the incident took place.