PITTSBURGH (AP) -- Gregory Brant found himself barricaded in a first-floor waiting room at a University of Pittsburgh psychiatric clinic, hoping he wouldn't be shot. For 15 minutes, it was fear and pandemonium.
A man armed with two semiautomatic handguns entered the clinic lobby Thursday afternoon and opened fire, killing one person and wounding several others before he was shot dead, apparently by campus police.
Authorities don't know why the shooting happened and released no information on the gunman. Officials said it appears he acted alone.
Six people were wounded and a seventh person suffered unspecified injuries. All are expected to survive.
"We heard a bunch of yelling, some shooting, people yelling, 'Hide! Hide!' " Brant said. "Everyone's yelling, 'Stay down!' "
Brant, 53, and six other people, including a young girl and her parents, were in a waiting room at the Western Psychiatric Institute and Clinic when the chaos began. They cowered in a corner, hoping they wouldn't be seen. But the men in the room quickly decided that if the gunman entered, they'd rush him.
"We were kind of sitting ducks," Brant said. "Luckily, he didn't see us in there, and we didn't make eye contact with him."
Mayor Luke Ravenstahl stopped short of confirming the gunman was shot by a University of Pittsburgh police officer. But he added that "police acted admirably and did engage in gunfire."
"There's no doubt that their swift response saved lives today," Ravenstahl said.
Officials at the University of Pittsburgh Medical Center said they were treating five patients aged 35 to 64, including two who had undergone surgery. A 64-year-old woman and a 49-year-old man were still listed in serious condition Friday morning.
Two others were treated and released, according the hospital officials. Their names were not disclosed.
One of the injured was a police officer who was grazed by a bullet. The injured people included employees and a visitor, said Dr. Donald Yealy, chair of emergency medicine at the university's medical school.
The clinic is a couple of miles from downtown, near the heart of the Pitt campus and its affiliated medical center.
Pitt sent out email and text alerts shortly after 2 p.m. to warn people of the shooting.
"An active shooter has been identified at Western Psychiatric Institute. Several injured," the alert said. "Possible second actor in Western Psych. Lockdown recommended until further notice. If safe to do so, tell others of this message."
Reports about a possible second gunman and a hostage situation at the clinic or at a nearby hospital were unfounded, UPMC spokesman Paul Wood said later.
Ravenstahl said authorities are still investigating whether the gunman reached the second floor of the clinic building, since there were reports of shell casings there.
SWAT teams shut the street off and adjacent buildings were put on lockdown. But a few blocks away people went on with their business. Most students are on spring break, though offices and buildings are open.
UPMC chief executive Jeffrey Romoff said the health network was "deeply, deeply saddened by today's events" and expressed "deepest sympathy to the victims and their families."
Lawton Snyder, executive director of Pitt's Eye and Ear Foundation, said he and two other staffers were locked down about a block away, in a building that connects to the clinic. He said it was unnerving and that he was "terribly sad for those injured."
Pete Finelli, who lives two blocks from the clinic and once worked there as a nursing assistant, said there are always security guards on the ground floor of the building, where the shooting occurred. That's also the equivalent of an emergency room, and is where patients are admitted and discharged.
Shaun Lorentz's wife, Melanie, works inside the clinic building. He said he's seen patients in the lobby who get irate because the facility doesn't have the resources to meet all their needs.
"A lot of mental facilities have closed" in the region, he said, and the remaining ones struggle to cope with the workload.
The psychiatric clinic has 292 beds but reported more than 372,000 outpatient visits and just over 11,000 emergency room visits in 2010, along with $79 million in research funding.
The University of Pittsburgh Medical Center asked that people avoid the clinic while the investigation into the shooting continues, but two nearby hospitals, UPMC Presbyterian and UPMC Shadyside, are operating normally.