A third possibility is that using timers to detonate the bombs might offer them some belief that they weren't actively committing suicide. Doubtful, I admit, but people who do such things operate with a different mindset from the rest of us.

Years ago, I heard a story about the first and most controversial FBI Director (J. Edgar Hoover). The story goes that on of his investigators was trying to understand the mindset of some sociopath. Hoover reportedly said, "Don't try to get into the mindset of a sociopath, or we'll have to worry about you."

Not that I agree with that sentiment, but there are some people out there whose frame of reference is so out of kilter with ours that we may never be able to understand them. The best we can hope to do is stop as many of them as possible and minimize the damage from the rest.