You must give the police credit they know how to make people confess. A retried German police was shoot dead in Thailand. The Police suspected the former wife and after asking her for 6 hours she confessed and she named her boyfriend as well. They then both named a French guy for doing the shooting.
In most cases with Thai murder if the Thai police have a suspect they get them to confess and sure you get a lot less sentence if you confess and life time can be reduced to 50 years and death can be life if you are helpful. You will get no deals like in America but the judge if he like you will always be nice to people that helped out and felt remorse, cry a lot helps.