I thought /u/shrikezero was saying the acts in OP's story were Lawful Good, and that's what I was referring to. Missed that he was replying to another comment, and I tried to note that in an edit. What he was actually referring to is Lawful good played right.

Op's main story though. I would consider Lawful Evil. Sure it's Lawful if his code allows him to torture, but just because a person thinks what he does is good does not make it good. Doing things for the greater good is an excuse. Dnd has a set good and evil, and youre going to be extremely hard pressed to find a society that believes torture is a good act. Necessary, sure, but good? No. I personally think what OP did in the main post to be worthy of an alignment shift from good because I can't really think of a worse form of torture aside from cutting off body parts. Killing a paladin serving an evil god? Good. Killing a captured paladin of an evil god? Grey area, but I could see it as good. Torturing said paladin, killing him, and healing him so you can continue the torture? Thats BBEG levels of evil.