Reno Police Chief Steve Pitts said John Dennis Gillane, 45, hid in a staff restroom after purchasing a 50-round box of 44-caliber ammunition from the store, the Reno (Nev.) Gazette-Journal reported Tuesday.
When a supervisor arrived, Gillane left the restroom and pointed a gun at the man.
Pitts told a Monday news conference Gillane demanded that the supervisor summon two more managers and then shot all three of them.
One manager was hit twice in the torso, another was shot in the leg and a third manager was hit once in the torso.
Hostage negotiators and crisis intervention officers persuaded Gillane to surrender Friday afternoon.
Walmart officials said there were no plans to fire Gillane before the shootings and it is unknown why he chose that day to air any grievances.