My concern about the toy remote triggering device is that there were two bombs. How far apart were the bombs? Did they have to use two separate transmitters given the proximity? Most of the cheap remotes don't have a great range so I guess they could have set the bombs off the same remote and spaced them so that they would blow at the same time but when the second didn't blow, the trigger man had to get closer to set it off. My guess is that they used a separate guy to run the trigger after they dropped the bombs and he got too close.
I know with my helicopter ( similar remote system ) it can fly out of range and I suspect the cars are the same. Interesting. Strip out the battery and pc board, attach it to a proper fuse system, and you are good to go boom. (Wonders how much the pressure cooker cuts down the signal).