[FlamesAddiction]

There are also reports that Matt de Grood had documented mental health problems in high school (not verified, but a few media sources have made those claims).

I won't even begin to make assumptions on his state of mind at the time. Mental illness may or may not have been a factor. Like Dissentowner said, mental illness is extremely complex and doesn't always show obvious signs. Someone with mental illness can "snap" or they can pre-meditate (just like anyone else). There is no template for these things. And just because someone with mental health issues commits a criminal act, it doesn't mean that they weren't rational at the time of the act. I am interested to see what the investigation indicates in this particular case.

People would probably shocked to find out that people they think they know really well, have been evaluated and/or treated for mental health issues in the past. For most people, those issues are extremely private and they don't walk around volunteering that information even to their closest friends.