The priest has to have a good reason completely separate from the confession for acting on the information he’s given, though. Depending on what this information pertains to, it may or may not be possible for the priest to have a good reason. If the bomb is in the priest’s own church, then it’s his church, he could find some reason to look through his own church without arousing suspicion. If it’s the church 10 miles away then it’s not that easy.
I can see where some, perhaps many, priests would choose to just not get involved. It’s not unlike similar situations involving lawyer-client confidentiality. Many lawyers would probably choose to just do nothing, assuming the alleged bomb is not menacing their own office or their own family member.