When my son was younger, he gets annoyed with security guards in the mall. He doesn't understand why they just let him in without inspecting his bag. Whenever that happens, always actually, he opens his bag and tells the guard to check his bag.
My bag? They inspect it by sticking a stick inside and abruptly removing it like they got burned with something from inside the bag. It's really not mind boggling why robbers are not at all scared to bring deadly weapons inside the mall. Everytime an "incident" happens, like the Glorietta bombing, the mall security thoroughly inspect the bags of mall visitors. And then they go back to their old lazy habit after a few months.
The mall management should not rely fully on security guards from preventing robbery or any bad incidents. They should install the best metal detectors available in the market these days to protect the mall-goers. They should have their customers best interest at heart and they should remember that bad things happening in their mall is bad for business.