It's an old post but, while I understand your skepticism, please do not suggest that Colleen is at any way at fault for Tom's actions. As someone very close to the Hemming family, I can assure you that Colleen has always been as supportive to Tom as any mother could possibly have been, still even now. And while his family life did not come without its fair share of bumps along the road, it was extremely far from "serious dysfunction".
It has already been stated by someone else, but I will reiterate the fact that this came to a total shock to everyone who knew Tom, including his parents and family. Personally, I didn't believe it until I saw his name in the newspaper, because it was just so unexpected.
To my surprise (and I'm sure many others), the neighborhood has been very supportive to both the Adamson and Hemming families, despite everything. If those living next to both the victims and the perpetrator, many of whom saw Tom grow up, can understand that Tom's actions were his own and in no way reflect on his parents or his upbringing, I'm sure you are able to give them the benefit of the doubt.