Notice how Rosalind Harker has never mentioned Roy Tagliaferro has an odd voice--that's probably cause he doesn't. An odd voice would be hard not to notice, specially by Harker who has all her other senses but vision heightened. Roy Tagliaferro is not the same man who killed those kids copying his work--cause that one had an odd voice--and he's also not the guy who met the little girl in the park (Red Rover, Red Rover)--she also mentioned the odd voice. So probably the one who shot those kids is the same guy who met that little girl, but Tagliaferro is someone else.