Did I garble that? A deadman switch is usually momentary open, normal closed. wire it in with your thumb off the button and complete the circuit as you fasten the lead.
The live switch would be normal open, momentary closed (push the button) or a simple toggle (flip the switch).
Other types mentioned were my musing that the unexploded devices which were reported in an earlier post to have been gathered up for study might have been intended for the busses.
If that was the case, then he might have had several devices rigged with either timers or motion activated switches.
The simplest of the latter would be safe as long as a seperate switch to arm the circuit was open.
If, however that device was at the wrong attitude in the pack, and the arming switch were inadvertently closed, the device would go off.
Just one possibility, especially as most vest type suicide bombers attach nails or other junk to the outside of the vest to get shrapnel, and there were no acounts of shrapnel, only blast effects.
The guy is a Mechanical Engineering student, chances are that the device would be tailored to the intended task.
No shrapnel? May have been intended to be attached to the busses' fuel tanks to increase the effect...