In the links provided, the violence was a result of conflict, or an argument, but no details are provided about the reason for the argument. Was it filthy personal habits, missing money, failure to participate in chores, using the residence as a party spot? "Conflict" or "argument" does not tell me anything about motive.
The prosecutor in this case has said that there was a conflict, or an argument. However, he also suggested the origin, or motive, in that conflict.
The term "argument" is not motive. The reason for the argument is the motive.