When a child is raised in the worst neighborhoods in a life of poverty and deprivation we must expect these things to happen.
They had this child from the age of 3, he was raised in a great neighborhood and not in poverty!
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.