Normally I get so annoyed by the perspectives of the relatives or the people who grew up and lived with the perpetrators because most of the time the giant red flags were always there waving right in front their faces. Not with this case though. A lot of what Mark did could be misconstrued as PTSD because his actions were unusual but not out of the realm especially with someone who has been in the military during a time when the world was so charged and people lauded these man for joining the military and fighting for their country but not at all thinking about the ramifications of what it was like to come back after having served .
A lot of his actions could have been attributed to him being just a stickler for rules and structure, being environmental and chemical conscious and having OCD and I definitely agree with the brother that if he was studying full time and working nights, he barely was interacting with him on a deeper level. He barely even had the time to notice all the little weird things that Mark was doing cause his life was taxing but also Mark had delineated these boundaries that he was not supposed to cross.
I do think that even though Mark seemed to be a nice kid when they were growing up, he definitely had issues with women and how he viewed them. He might not have always voiced them and he might have said a misogynistic thing here and there like many men do but we never think that these men will go out and start raping women. It's interesting that most of his victims were older women . Probably easier to incapacitate and might have less power to scratch and bite thereby leaving his DNA there. He definitely got off on control more than having a type.