RENO, Nev. - A gunman who police said was about to be fired surrendered Friday after shooting three co-workers at a Walmart store in Nevada in a possible retaliation attack, authorities said.

The peaceful surrender capped a six-hour standoff during which police negotiators said they spoke by telephone with 45-year-old John Dennis Gillane as he was holed up in an office in the store.

Gillane was taken into custody and will be charged with three counts of attempted murder, Reno police Lt. Mohammad Rafaqat said.

No shots were fired after the three male victims, including a manager, were wounded shortly after 8:30 a.m., police said.

"I'm very happy he is out and the situation didn't escalate," Rafaqat said. "We convinced him the best move was to surrender."

Rafaqat did not know how many shots were fired or whether anything was said at the time of the shootings.

"Today was going to be the day he was going to address his employment situation," he said.

Police had not established a motive for the shooting but suspect it was related to the termination, Reno Deputy Police Chief Mike Whan said.

"He's not admitting that right now, but we can assume that," Whan said.

Rafaqat said investigators had not determined if the manager who was shot was Gillane's supervisor. The shootings apparently took place in rapid succession near a management office, he added.

A SWAT team entered the store more than three hours before the surrender of Gillane, who police believe had a handgun.

One victim was treated and released, Rafaqat said. Another was in critical but stable condition, and the third was in serious condition.

"The prognosis is good for all of them," said Dan Fogleman, a spokesman for Wal-mart Stores Inc. He provided no further details.

Fogleman also declined to comment on Gillane's possible pending termination or his relationship with the victims.

Lorenzo Lopez, another spokesman for Wal-mart Stores Inc. in Bentonville, Ark., said the company would not comment on personnel matters and had no new information on the shooting victims.

Employees were taken to the parking lot of a sporting goods store next to the Walmart and interviewed by police detectives.

Walmart managers directed employees not to talk to the media and referred inquiries to the company's media relations department.

Earlier, Washoe County deputies, Sparks police and the FBI had joined Reno police in sweeping the store to be sure there were no hostages.

Jack McDonald, 64, of Reno said he works as a greeter at the store but was not there during the shooting.

"There are some strange people who work here, but I can't think of one who would be a vicious enough person to do something like this," McDonald said. "This has to be a personal thing."

McDonald, a neighbor of the store's general manager, said the shootings shocked him.

"I've never worked for a place I've enjoyed so much," he said. "All the managers treat us fairly and professionally. I can't think of a single person in the store who deserves this."