The only one who knows his motives is him. Has he done this before or was it just him picking up a girl with an intent to have sex? Did he pick her up with dark intentions from the start? Did it have nothing to do with money as 500-1000 Baht is accepted prices here for some, and coming here he likely had already heard about it? Did a fight start about that little sum of money, which is unlikely, and did the girl pull a knife like he said or just an argument where he grabbed her by the neck and took it all the way, not able to stop for reasons known only to him? The fact remains if things got out of hand, and he can prove about a knife, then it was un intentional from the start and he went too far when she pulled that knife, but he should have then went to the police with his story. Did he fear no justice from local police, that he wouldn't be given a fair trial, or is he a murderer already, that this wasn't his first charade? The other fact, hiding and disposing of her body shows guilt where he didn't want to face anything but just wanted to leave Thailand. Was he afraid of not being given that fair trial or is he a cold blooded murderer? All this is guesses, like all others here, and until the evidence comes out there's no way of telling. If this wasn't Thailand, would justice be served differently? Of course, even though the justice system here is supposed to mirror the west, pleading guilty will get you a reduced sentence a lot easier than in the west. Is he pleading not guilty because he feels she attacked him and it was a kind of self defense, or was it just him going overboard about something minor where he couldn't or didn't want to stop? If he's guilty, it should be life in prison, as the death penalty won't be acted upon here. Him being caught might have already saved lives.