"Why not just drop a piano on him and pocket the difference?"
Exactly right. This wasn't a "statement assassination,"- it was far worse: 1 gram of Polonium can kill 100 million people. It took a speck less than 1/10 millionth of the size of an aspirin to kill this "spy." If I lived in the UK or Russia right now, I'd be extremely worried about where the rest of this stuff is. In fact, I'm not feeling too secure here.
Dumb, dumb, mind jumping speculations...
When did the ban on liquids take place? Doesn't Polonium 210 vaporize in air? Wouldn't this be transported in liquid?