(CNN) -- A gunman who opened fire on his co-workers at a Walmart in Reno, Nevada, was arrested without incident Friday after a six-hour standoff with authorities, Reno police said. Three employees were injured and two remained hospitalized Friday night in serious to stable condition, Lt. Mohammad Rafaqat told CNN. John Gillane, 46, will be charged with three counts of attempted murder in the shootings, Rafaqat said. The incident began at 8:30 a.m. (11:30 a.m. ET) when Gillane walked into the store and opened fire on employees before barricading himself in an office. It ended at 2:30 p.m. (5:30 p.m. ET) after hours of police negotiations. A possible motive for the attack was not immediately clear, Rafaqat said. "Our thoughts and prayers are with our employees at this time," Wal-Mart spokesman Dan Fogleman said. CNN's Sara Pratley contributed to this report.
NEW: Three employees are injured in the shooting by their co-worker, police say . NEW: John Gillane will be charged with three counts of attempted murder . NEW: Two people remain hospitalized in serious to stable condition .