Police officers' swift response in Thursday's shooting saved lives, Pittsburgh's mayor said.

Story highlights

NEW: Officials search suspect's apartment, source says

NEW: One of five hospitalized patients released

Michael Schaab, 25, died after being shot by the gunman

Those who remain hospitalized are all employees of the psychiatric hospita

CNN  — 

Police on Friday identified the gunman who walked into a Pittsburgh psychiatric hospital and started shooting as 30-year-old John Shick.

Pittsburgh police Cmdr. Thomas Stangrecki initially told reporters that attempts to name the man, who was not carrying identification, had failed. But later Friday said authorities had determined his identity and were reviewing his personal computer as part of their investigation.

Shick was shot and killed by police Thursday, but not before he killed hospital employee Michael Schaab, 25, and injured seven others.

“It was clear that Michael was truly a leader among our staff, and he was beloved by the geriatric patients whom he cared for every day,” said hospital President Claudia Roth. “Our thoughts and prayers are with his family and friends during this time.”

Roth called the incident a “senseless act of violence” that “has had a profound impact on all of us who knew and admired him.”

“He will be greatly missed,” she said.

A law enforcement source told CNN’s Susan Candiotti that Shick is believed to be a transient from the western United States. Shick’s Pittsburgh apartment was being searched Friday evening.

One of the two 9mm handguns recovered was traced to New Mexico and the other was traced to Texas, the law enforcement source said. It was not known whether the weapons were legally purchased or how Shick allegedly came to have them.

Investigators also recovered an extra box of ammunition, the source said.

The guns generally hold about 15 rounds. It remained unclear how many rounds were fired before the suspect was killed by police.

Four people remained hospitalized Friday, according to hospital spokeswoman Wendy Zellner.

They include a 46-year-old man listed in fair condition, a 64-year-old woman in serious condition, a 35-year-old man in good condition and a 49-year-old man in serious condition, authorities said.

A 54-year-old woman was released from the hospital Friday.

“This is a tragic day, a sad day, a senseless day,” Pittsburgh Mayor Luke Ravenstahl said after the shooting Thursday at the medical center.

The assailant walked through the psychiatric hospital’s front door with a pair of semi-automatic handguns around 1:40 p.m., according to Ravenstahl.

Officers from the University of Pittsburgh Police Department arrived within “a matter of minutes” and “engaged” the gunman, the mayor added.

“There is no doubt that their swift response saved lives today,” said Ravenstahl, lauding the police officers’ “courage and willingness to step up.”

Those wounded were swiftly ushered to nearby UPMC Presbyterian. All are expected to survive.

Officials said two of the five hospitalized patients have undergone surgery.

iReporter was on the scene

Ravenstahl said that a University of Pittsburgh police officer “was grazed with a bullet, and I believe he is doing well.”

Steven Bartholomew, a spokesman for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives, said his agency is “working with Pittsburgh police and other authorities in the investigation.”

“Any firearms recovered will be traced to determine their source,” Bartholomew said.

At one point Thursday, the University of Pittsburgh’s official Twitter account had a message that suggested a “possible 2nd actor” was involved and called for a lockdown.

But later Thursday, the medical center’s Twitter feed had a message that “there was no second shooter” and there was “no hostage situation,” as had been reported elsewhere.

Roth, the psychiatric hospital’s president, said after the shooting that treatment at the facility “will be uncompromised,” with care continuing to be delivered through the day and night “the same way we always have.”

CNN’s Jeremy Ryan contributed to this report.