A few months ago, security found a propane tank bomb at the local coal-fired steam plant in Centralia, WA. It was a 5-gallon propane tank with some kind of black powder/electronic detonator. Less than ten days later, they got the guy who made it and put it there.
Here's the guy's story: He made the bomb as entertainment for the Fourth of July. He tried to ignite it, but the black powder was apparently the only part that ignited. He said he kept it around at home for a couple of months, then decided to take it twenty miles away and dump it near the steam plant/coal mine. It was just a holiday prank, honest!
Can you imagine what the neighborhood would have looked like had it worked as he intended, with all the kids around? But I don't think anyone really believed his story. Of course, it's possible that he's the craziest, most ignorant person on the face of the earth...
Sue