Philadelphia ? Two armored car guards were shot and killed by a robber as they removed deposits from a bank ATM in a brazen daylight heist Thursday, setting off a sweeping search for the killer that shut down a nearby mall and several schools.

After hours of searching, authorities had few leads and only a sketchy description of the gunman, who police said approached the guards and fired without saying a word.

The robber approached the car from behind shortly after 8 a.m., shot one guard in the chest, then went around the vehicle and shot the second guard as he tried to unholster his gun, police said.