An excellent episode... except for the unbelievable motive.
The most unbelievable thing about this episode is the fact that they use a car alarm key fob in the 90s through several floors of concrete and steel to activate the gun firing mechanism when my key fob won't work from the other side of an open air parking lot in 2025.
I'm not going to worry too much about the distance between the lecture hall and the truck in the garage.
Maybe it's directly below them... we really don't know. Just assume it is and go with it! Or maybe they installed an antenna or amplifier. I wouldn't worry about it!