What a wonderful question on the culpability of autistic people regarding sin. While I always had to a degree the view that Joe mentioned - Joe actually gave me a lot of peace of mind regarding my autistic son. While I did a lot of work with my sons specialists when younger to get him to a place where he can cope day to day where others wouldn't realise he is autistic unless they got to know him or knew the subtleties of autism he still needs a lot of support and still has the very black and white thinking which can be hard to break him from when someone had given him bad spiritual advise for example in confession and trying to get him to understand the nuance on the faith
CATECHISM OF THE CATHOLIC CHURCH: “Responsibility for an action can be diminished or even nullified by immaturity, force of acquired habit, conditions of anxiety, or other psychological or social forces.” ST. THOMAS AQUINAS: “Because of the diverse conditions of humans, it happens that some acts are virtuous to some people, as appropriate and suitable to them, while the same acts are immoral for others, as inappropriate to them.”
MATHEW 16 :18 JESUS SAID I WILL BUILD MY CHURCH UPON THE ROCK AND THE GATES OF HELL SHALL NOT PREVAIL THROUGH THE APOSTLES CARRIED OUT JESUS PLAN OF SALVATION AS STATED ABOVE