Not necessarily. Being very involved in organized religion and being religious are two different things. Perhaps "spiritual" is a better word than religious. I have long turned from organized religion but I am still a spiritual person. Yet the lack of religion or faith in God wouldn't seem to me to make a person more likely to believe the parents did this. Neither would their religious affiliation or how devout they were in its practice imply the opposite (to me). However, people like LS, who seemed to be as devout as the Rs seemed to be might be swayed by that. It is hard to stay impartial when this fervor is shared by someone you are trying to implicate in a crime like this. Some of the most heinous crimes are committed by religious people. Hitler was a Christian, too. Religious wars, including the Crusades, have perpetrated terrible acts. Being an atheist may imply that no punishment awaits in the hereafter (actually, the hereafter wouldn't exist either), but I don't see much evidence of that being the motivation for committing horrendous crimes. I think as far as the Rs and LS go, it is far simpler. He felt a religious "kinship" with them, and that clouded his ability to consider that they did this.