I'll have to edit that part out. 

Adam didn't feel much after witnessing the girl's death.

No wonder this is such a deeply rooted memory in his mind. This is most likely the first time that he killed someone, and the special combination of anxiety, fear, and sadistic euphoria must've made this a very memorable experience for him. 

It seemed that in order to find the root cause behind a heinous criminal's descent into depravity, it was always a good idea to search for deeply rooted memories from their childhoods.

The vast majority of people only had very indistinct memories from their childhoods, and the only childhood memories that were very clear were generally ones that were extremely impactful, thereby making them very good starting points for investigations...