The bomb squad blew up the bag, but found no explosives.
How are you gonna find explosives if you blow them up?
;^)
You use a remote explosive device to open the bag, this can be done by a slug or a shaped charge. If you do it right, normally it will not set off any explosives inside. Used to do it all the time. I have a good friend that tried that on the Casino in Lake Tahoe, things didn't work out very well there.