Lawrence police are investigating the overnight armed robbery of a Wal-Mart. Police said a heavy-set white man armed with a gun robbed the store on Pendleton Pike near Sunnyside Road about 2:45 a.m. Tuesday. The man forced two cashiers to empty their registers, an employee said. The suspect escaped in a dark blue Ford Taurus. Police are reviewing surveillance video. Fox59 will have more at 4 p.m.