Unfortunately, they don't know what they are doing rendering it useless.

If I were a bomber:

1. I'd put the C4 in the spare tire, park it in the mall and leave it to detonate.
2. I'll put it in a laptop and detonate via cp.
3. I'll put in a flower vase (with soil on top) or inside a similar kind of inconspicuous cylinder.
4. and so on.

If I were a mall owner or chief of security:

1. I'd put x-ray on all exit and entry points of my mall.
2. Hire at least three people whose job is to watch the surveillance videos all day.
3. Donate to the military's anti-terrorism campaign.
4. and so on.