So he harmlessly killed those people. How? And if you're going to say he didn't physically drive the trains into each other, how far does that rabbit hole go?

So he harmlessly killed those people. How? And if you're going to say he didn't physically drive the trains into each other, how far does that rabbit hole go? Can anyone be held responsible for any action performed with a tool at that point? "Your honor, I just caused a collision of his head with this hammer, it was the hammer that killed him, not me." Oh, he swung the hammer, so that counts as "physical harm". What about guns? "I just caused a collision of his head with the bullet, the bullet killed him, not me." Yes, he would have pulled the trigger, but he didn't physically shove the bullet into the guy (by your definition). Or if pulling the trigger makes him liable, then the guy pressing the keys to run the programs blah blah blah that cause the trains to collide means he caused it. In your case, he engineered the deaths of the people on those trains, he's liable for them. This ain't hard.