Updated at 1:46 p.m. ET
(CBS/AP) Pittsburgh's police chief said a military veteran was holding an office worker hostage inside a downtown office building and was talking with police negotiators.
The man took the hostage shortly after 8 a.m. on the 16th floor of Three Gateway Center, one of six office buildings that dominate the city skyline, Police Chief Nate Harper said.
CBS Pittsburgh station KDKA-TV reports that police have identified the suspect as Klein Michael Thaxton, 22, from McKeesport, Pa., which is outside Pittsburgh. Earlier, Harper described the suspect to reporters as "ex-military," but didn't elaborate. He also said the suspect had a criminal background.
Harper said the man entered an office suite and asked about a particular person. He then said he had a weapon. Harper said he didn't know what caused the man to take the worker hostage.
"No one knows why he's doing this except him," Harper told reporters.
Thaxton apparently started posting status updates to his Facebook page at 8:54 a.m. ET and continued posting until 11:18 a.m. ET. One update posted to his page read: "this life im livn rite now i dnt want anymore ive lost everything and i aint gettn it back."
The page was taken down early Friday afternoon.
"welln pops youll never have to woryy about me again you'll nevr need to by me anything no need to ever waste ur hard earned money on me. i'll live n jail you dnt want me around anymore thats kool bye," read another update.
Harper told reporters that he discouraged people from communicating with Thaxton over his Facebook page, saying that he wanted the suspect to only be talking with his negotiators.
Harper said no injuries had been reported and no shots had been fired.
Harper confirmed to reporters the hostage-taking unfolded inside the offices of CW Breitsman Associates, a firm that runs employee-benefits programs.
Harper said the man isn't an employee at the firm. He said the suspect was cooperating with negotiators and is "not being irrational."
"His demeanor is, from what I understand, relatively calm, and he's sitting there talking to the negotiator at this time," Harper told reporters.
Thaxton's friends responded to his Facebook postings by urging him to end the situation peacefully, including one who asked him to think of his mother.
The Facebook postings have the potential to both help and harm the negotiations, Harper said.
It's helpful that Thaxton can see "that people are concerned about his well-being," Harper said, but "it is a distraction for negotiating."
As the situation unfolded Friday morning, Kathi Dvorak, an administrative assistant at AXA Advisors, said a woman ran into her office yelling for someone to call 911. A second woman ran in and said her office was being robbed.
Police arrived soon after and began evacuating the building.
Several hundred people milled around about a half-block from the 24-story building after police evacuated it. A light rail stop nearby was closed and at least 20 emergency vehicles surrounded the building.
Joel Kirchartz, a 28-year-old web developer who works on the 17th floor, said he and his co-workers looked out the windows Friday morning and "a bunch of cops pulled up with all sorts of sirens going; there must have been 20 of them." He said he went downstairs to find out what was happening and by the time he got outside, police had sealed the building.
Another worker, Sarah Vereb, said she was at her desk when she was ordered to leave the building shortly after a friend called to report that she wasn't being allowed up from the lobby.
Hundreds of workers walked down the stairwell. Vereb said the exodus was orderly and "very, very quiet."
A phone message left for the building's Santa Monica, Calif.-based ownership group was not immediately returned. The building complex management office confirmed the evacuation and said it was working with police.