IMO, we're not talking 'someone' here, we're talking 'son'.
It is inherent to parenthood to support one's offspring: regardless of what has happened in their life, one's parental duty is to, for example, allow them to come back home to live, give them the name of the family lawyer if they ask, etc. Similar with other family members: spouses, grandparents, etc.
This is done with or without knowing why. With or without approving of what happened.
This is, IMO, why prosecutors rarely charge family members with accessory unless they actually helped move/conceal the physical remains.
IMO, unless we make it illegal to assist one's grown child until one first ascertains why, exactly, they need assistance and that no criminal actions were involved, and we make it obligatory for offspring to submit a signed statement in writing as to why they require this parental assistance, which the parent must preserve and submit to legal authorities if questioned, then we cannot charge parents with accessory after the fact.
JMO