I assume they had an electronic timer to trigger a blasting cap. Read somewhere they identified manufacturer of the battery that was used.
Short leads on a electric blasting cap could have been used with an internal timer in the bomb. That would reduce stray pickup on wires in the system. Have heard that we used generator systems in sandpile to detonate some of their IEDs.
Hand placing the explosive has some risk for the one who delivers It.
curious- how did the obama-protected Saudi dude get burned hands as his injury?