The killer was adopted at the age of three. He may have had a terrible childhood before then, but I do believe there are inborn tendencies in people, and that very sadly, adopted children are more likely to be afflicted with mental illness and pathological aggression.
Their mothers may have given them up because they themselves were mentally ill, or lacked all maternal feeling. They may also have given them up because the father was very bad news. The babies may have been affected by maternal drug or alcohol abuse. This is especially true in a society when adoption is not the usual solution to unwed pregnancy or poverty as it was in the past.
A disproportionate number of serial killers are adopted, although one researcher claims that is because of the primal trauma of adoption.
Of course there are many healthy, wonderful people who have been adopted - and there are biological families who have their own inherited problems - but then you are more prepared for what you get.
I’ll add one thing: little Mr Murderer got raised in a hell of a lot better economic environment with wealthy physician daddy than me and my seven younger siblings did And I bet he didn’t move twelve times by the time he was 18 like I did.
We don’t know if he was a real rat or if the sister was really obnoxious or what. Not that that would excuse him.