Complex sentence: Lanza was diagnosed with a sensory-integration disorder when he started elementary school and was later diagnosed by a psychiatrist with Asperger syndrome when he was thirteen, according to his father, Peter Lanza.
Split into simpler sentences: Lanza was diagnosed with a sensory-integration disorder at the start of elementary school. When he was thirteen he was diagnosed by a psychiatrist with Asperger syndrome, according to his father, Peter Lanza.