Howard made it so complicated....but so orderly that it's gonna hang him. Hell, he couldn't even think of two different ways to kill them.
As I said before, the fact that two deaths of two related persons dying in different places within the same small timeframe (1-2 hrs max)is astronomical. I'm a mathematician by profession. (I'm still considering death via inhalation....the quickest way to get something directly into the bloodstream.)