Yeah, it's tricky sometimes. Husayn's death doesn't quite fit an execution I think as there was fighting and he was not tried in any way before being killed. Rasputin likely died from a shot and was already dead when they threw his body in the river. And I'm counting Rommel's suicide as forced as he was told he could either kill himself or be executed, so he didn't really die of his own will (hence the caveat).
Rasputin was assassinated but also technically drowned so I feel like it's not a clear answer.
Rommel actually committed suicide before he could be officially tried and executed.