Think back to the Olympic bombing in Atlanta. The FBI tried to frame Richard Jewell by asking him to be part of a "Training Demonstration".
This could be the same type of frame up for a Training Op.
All you need is two rogue undercover FBI Agents to friend this guy, they talk him into the crime and tell him how to do it so he never gets caught.
Remember this guys a few crayons short of a full box. All the sudden he’s got two new buddies who help convince him he’s the guy to do it and have him make these dud bombs and they also happen to have the addresses for him too!!!!
How convenient huh?... just sayin...