Perfect Crimes

A friend of mine used to be part of a gang of eco-terrorists. He and his cohorts used to put timed destructive devices in backwoods buildings, structures they maintained shouldn't have been built in the first place.

Their technique was simple: they simply placed pine cones--or was it seedlings?--at structurally critical parts of the building. By the time the roots had damaged the building beyond repair, they already had made their escape some years earlier.

They were very clever; they never got caught.