Why did he kill the hotel clerk?
Anton tracked him down at two hotels. The first he takes his time. He goes to the desk and orders a room next to the room he's tracked the money to. He plans his entry and scopes the layout of the room so he'll know where to aim quickly and where the hiding spots are. He has no issue with the desk clerk.
Then he tracks him down at a second hotel. This time we know Llewelyn knows he's there and is coming. So if Anton had taken the same action things would have turned out differently. This time he kills the desk clerk. Why? Then instead of ordering a room and plotting the room layout he just goes right after Llewelyn as soon as he enters the hall.
Why the sudden changes in behavior and killing of the desk clerk?