“Why would a setup NOT include a power source?”
If there are bulk scanners (CT scanner or the like) with Automated Threat Detection algorithms, they will likely trip on suspicion of explosives if there is a power source.
Bomb people look for a “firing train” and power source as much as they look for explosives themselves.
Ship them here, then add the 9V battery, arm, and deliver. I think you have it right.
No way was this a “dry run”, someone either twigged to it or some scanner caught some. Why in the world risk exposure through a dry run?
Addressed to the target? Unless they have a jihadi inside the Synagogue.