Get back at trevelayan!
I have discovered several ways to torture trevelayan.
Alec torture tactic #1: activate the all weapons cheat, invisibility cheat, and the infinite ammo cheat.
Then go to the caverns level, and when you get out of the elevator, there should be 3 guys standing there.
Go to the third one and it is trevelayan! He is invincible now, but you can still have fun shooting him and blowing him up! Alec torture tactics 2, 3, and 4: in the facility level kill trevelayan and he will say, "so the golden boy is a traitor, eh?" funny I guess.
On the train level, in the room with natalya being held hostage, fire a round of anything exploive into the room and trevelayan and xiena (zee-na).
Finally, on the statue level, when you get to the part where you rendevous with alec, run towards him and follow him. He will eventually stop and start running against a pillar.
He is glitchy and just begging to be filled with lead. Enjoy!