People like this are defective or damaged. In that sense they are not criminal as say a robber, because it is certainly the case of the two brothers they are not of sound mind.
The modern approach of living within the community is probably the real culprit. The closure of the Victorian institutions when damaged folk could live out of harms way, under full time supervision was the wrong move. The bureaucratic, computer-report, box ticking driven method that social works exist under instead of being Out in the field' Not that any social worker could keep track of of all their charges 24/7