Like I said, he could only be prosecuted for any crimes that he actually committed, and only if here in the US - not for religious beliefs, as religious beliefs are not crimes. You can have dreams of killing thousands of people as part of a religious ceremony, but unless you make plans to do so, you have not committed a prosecutable crime. The moment that a person formulates such a plan, you know that I am right there with you in calling for their trial and subsequent punishment f convicted.
So, do you have any reason to believe that Castro was secretly a Muslim, and was acting on religious teachings?