The mother’s reaction is not indicative of anything, at this point. She is probably in some state of shock, and people under this kind of stress will often react oddly.
Even if she knew something was wrong with him, we have no idea what that was. Maybe he was showing signs of mental illness. Maybe he had shown signs that he was becoming violent in his political beliefs. Maybe ... anything.
We don’t know anything definitive at this point. Speculation on mental illness is just as speculative as any other speculation.
I usually try to start off with a default state of mind regarding these things, and I feel sympathy for parents and relatives of the suspect.
If it comes out that the parents or family are radicals who imparted those values and steered a son or daughter down that path, then I will reconsider at that time.
Right now, I would assume the poor woman is in shock.
All I hear about is the mother, what about, where is the father?