Cassanova would definitely be a crime, firstly because the child would be bullied/teased every day of his life, and secondly because it's spelled Casanova.
Cassian,
Cassius, even Cassander are acceptable full names for the nn
Cass.
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.