[Smokin' Joe]

If he was using a motion activated detonator, and prematurely flipped the arming switch (even snagged it on the backpack) he could have easily blown himsief up. Other devices might not have gone off because they were not armed.

A motion activated trigger circuit would be child's play for a mechanical engineering student, and would be effective against a mobile target, once attached and armed.

Depending on the type of trigger, anything from starting the bus to going up a steep hill or hitting a bump would cause the bomb to go off.

[claudiustg]

I've seen the small reed switches that are supposed to detect when you close a notebook screen be defective present a permanently closed circuit. Putting one of those in your bomb would be very bad.

The Palestinians seem to blow themselves up by accident on a fairly regular basis and they have a lot of experience with these devices.