I would say Lawful Neutral or Lawful Evil.
If he's just drowing "puppies" then he could probably get away with Lawful Neutral. If was drowning people, then Lawful Evil.
I don't play alignments in my game and this is one reason I don't do it. You see, Myrddin, it doesn't matter what "alignment" your character is; you just play him how you *want* to play him. It sounds like you've got a great character concept going there, but to tag it with an alignment is not only unnecessary but it can create all sorts of disputes in the game.
Just take a look at people's opinions so far. Some say Chaotic Good, some say Lawful Evil, and I've just added another: Lawful Neutral. With alignment, everybody has a different opinion and if there's a differing of opinion then this can lead to trouble. Say a GM says your character is Lawful Evil but you vehemently disagree. You say he is Chaotic GOOD! This will lead to a dispute and resentment for the GM when he starts to penalize you for "evil" actions that you think serve the higher goal of "good".
This is one reason I don't play alignments. If you were in my game, Myrddin, and asked me "What alignment is my character?", I would not answer "LN or LE", I'd answer: "It doesn't matter, you just play the great character sketch that you've come up with and we'll let the NPCs in the game world judge your actions. People of your faith will call you 'good'; people not of your faith (and whose puppies your drowning) will probably call you 'evil'".
This way alignment becomes relative to the situation and not a game mechanic. And this is essentially why it remains in D&D, because it is a game mechanic that determines the outcome of spells like Detect Good/Evil and Holy/Unholy Smite. If you choose to have no alignment, then you can still keep these spells but they will need some tweaking. In the end, from my experience, the game is still 100% D&D.
