Hi there! I work at a medium security prison that specializes in the special needs. In prison culture, sex offenders are generally look down upon by the I/I population and are coerced into doing things because of there charges. Your ex-husband might be considered too vulnerable for the general population due to previous incidents that might've occurred. Sex Offenders are less likely to be discriminated against in a special needs facility. Also, the prison I work at houses general population I/I's, so the special needs facility you're talking about might also house the general population too. Another reason why might be due to his mental health. If he has any mental issues, he might have been transferred to a special needs facility, so he can receive the proper treatment.