I somehow think that unless this was a serial killer with no connection to either victim, then the hate was not directed toward Tom or Shirlee. It was directed to something they represented. Someone could have had hatred for the Hunter family or one of it's members, ditto for someone in Shirlee's family. My guess in this case would be that it was toward the boy's family. I say that because the Hunters were more prominent and moved in circles that could have harbored someone like this more easily. Someone with a mask of respectability, say- a friend of the family, a collegue. Someone who got passed over for a promottion at CU years before, perhaps even someone with ethical issues over something that may have been going on in the lab, who knows? In that case it was someone close to them, so close they do not suspect them. Someone who possibly is still in their lives and grieved with them. Killing their beloved child was meant to inflict pain on them.
Someone knew the schedule. They could have timed this to be when Claire was out of town. Either it was given to a hired killer or the person themselves knew when to strike.
