IIRC, b09, they have a daughter, too. Three children she bore for this animal to abuse. Not to mention, she left him alone with the now deceased child AND the one he had mutilated prior. She took their daughter shopping with her. It's not like she didn't know what he was capable of, IMO. How could she not know? I'm sure these two incidents weren't the only indicators.
I wonder if Samuel was severely abused as a child, himself. I wouldn't be surprised. Not to say all abused children grow up to repeat their abuse, but sometimes they do. He looks pretty scarred/beat up to me and, IMO, would be a prime example of those who do occasionally repeat the abuse that they endured as a child. Not that that excuses him by any means. It also doesn't excuse the 'mother', IMO.