If you take Scott's apparent personality (and of course none of us garnering our info from news accounts can ever TRULY know his personality), it would make sense that he would hire someone to rid him of wife and baby, rather than do it himself.I'm still not convinced that is what happened, but it is entirely plausible.
My theory is that he was seriously considering ridding himself of Laci, he was infact making preparations to do just that, but something happened between them that pushed the matter into his own hands...in other words, he killed her himself, but he may have had help in disposing of her body....