Lacking more specific information on the cases in question I can only speculate. However, their actions are consistent with those of a schizophrenic.
Very strange. The article said that the family was from Texas and owned a gas station or convenience store(I would assume they are Pakistanis, in that case)and bought the house a year or so ago, but they had nothing to do with the neighbors. Apparently they didn't put up window coverings until the neighbors complained about having to look at the ironing board the family had left set up in the living room for several months. It sounds as if the whole family was a little odd. If there even was a family - neither the killer nor his family is shown or interviewed, so it's hard to say who actually lived in the house.
One of the problems with Islam is that it is very hard to tell it apart from schizophrenia, of course. Personally, I think this guy was just out doing his own little individual jihad, and he was probably encouraged by his family. I attended the trial of a Pakistani convenience store owner in Texas who had made big money from his gas station and was busy putting it into a fraudulent transaction so he could funnel money off to Hamas to kill Jews, with the aid of a foreign national named Mohammed Islam, so nothing surprises me.
You might be right...this could be a case of schizophrenia, and the family, especially an Arab family where the male (sick one), is in total control, would be hesitant to seek help. But Islam, taken literally, promotes wholesale murder. At this point in the march of Jihad, what difference does it make if Jabbar is a schizophrenic who didn't take his meds? If it turns out the local mullah preached Jihad and influenced a mentally ill Jabbar to kill someone, who really pulled the trigger?