Given his age it’s possible (but a bit later than normal) he’s had a first paranoid schizophrenic break, which took his apparently fairly mainstream and non-violent conservative political views and twisted them into an obsession against the Norwegian Labour Party; however, the level of his personal planning and organization in the attacks seems to be a bit unrealistic for the condition; however, there are always exceptions and outlier cases in mental illness.
Well said, and a rational voice on a day when such is in short supply.
I remember a largely forgotten case in the middle of the 20th century where a deranged individual saved up or created explosives and attacked a school with severe casualties. It also combined elements of insanity and long-term planning. Rare, but it happens.
Agree with your hypothetical scenarios. Plausible...just no evidence yet.