He was killed by someone who carried pre-mixed nitroglycerine onto the plane. That threat is still possible because the WTMD does not detect liquids and that volume is concealable.

The problem with pre-mixed nitroglycerine is that it is so volatile that just walking around with it, or worse yet, having it near a 98.6 degree F human is enough to cause it to detonate. The terrorist got extremely lucky.

Anyone can kill 1 or 2 other people on the plane without nitroglycerine or other explosives at all. It's not a threat that is worth worrying about. Such a killing can occur at the mall, on the street, or just about anywhere else in the world.

We really need to get out of this safety at all costs nonsense because it's not obtainable or credible and focus on legitimate threats to aircraft, not individual people. If someone wants to kill another person and does not care about the consequences, they will succeed.