Remus isn't a half breed, being a werewolf doesnt make you a half breed. You can rule out Hagrid cause he is half breed, not half blood. Also someone pointed out earlier, Colin Creevy was attacked so he is muggle born. We can probably rule out Justin Flinch-Fletchly cause he said he was down for eton, but he made his mom read Lockharts books. She decided hogwarts cause it would be nice to have a fully trained wizard in the family. Well wouldn't they already have one if Justin was half blood? I'm sticking to Tom Riddle but if i find anything on JK's site i'll post it