I think two things could have happened... they were actually robbed and weren't after things, just money... I don't think they had much, but maybe they got into a fight over something small, were intimidated, and taken somewhere else... and the other possibility is that he was tired of taking care of his mother... maybe he was looking for a change... saw an interesting opportunity, or had already discussed it with his brother-in-law... whatever the reason,
rest in peace,
David