Remote trigger, timer, speed monitor, millions of easy ways.
Nothing so sophisticated, I'd expect: though professional spooks might- or might not- use such devices if they weren't concerned that there'd be clear evidence of such equipment left behind, particularly if foreign-made equipment could be used to point the blame elsewhere in a *false flag* operation, these guys are supposedly cut off from such support from embassy and other convenient means of smuggling such tech gear into a country. And the recovered Al-Quiada terror manual stressed the ability to create explosives and incendiary devices from locally available materials, such as those available from the average discount Mart-Mart, Home Depot, or, just for instance, a gas station. I can think of a couple of simple chemical compounds that would create a sudden and intense flame, and combined with a liter bottle of gasoline, would thoroughly incinerate the front seat occupants of a car if left under the driver's seat and the flames were confined inside, as in a car with the windows rolled up in the wintertime.
Hell of a way to die, frying alive. Doesn't say much for the 'brotherhood' of terrorists, does it???