The perp had a human mind and THIS compelled his heinous behavior.
Blaming genetics is specious because our DNA did not evolve to include a gene for slaughtering children.
We seem to be living through an unprecedented period of severe mental illness in every phase of our lives, from irrational violence to sexual "orientation" confusion to drug addiction to homelessness... etc.
We are born with our brain development unfinished and our minds totally blank.
It takes years for a human being to begin to function somewhat independently.
This growth occurs in the context of a family.
If the family is dysfunctional the person's mental, emotional and behavioral processes with reflect this.
As a species we deny this psychological reality... perhaps because it suggests some degree of trouble deep within all of our minds.
After all... no family is perfect.