They have not actually made a hard and fast connection with this being causative to the murders, but the doctor presented evidence of brain "damage" caused by multiple concussions. They stained sections of his brain with a dye specific to a protein that is present when brain cells are stressed, damaged or dead. The pathology looks similar to people with Alzheimer's disease.
Steroids did not cause him to commit murder. Neither did brain plaques. He was a troubled man with mental torment. Only an insane person at the end of their rope would murder their spouse and child.
IMO, I think they are looking for a physical cause for a psychological problem.
And no matter the outcome, the media will continue to demonize steroids.