You and your wife need to seek help from a criminal defense attorney in your area as soon as possible - like yesterday.  Your son is an adult (and this is not to say that she did not panic as a Mom; only that he is not a minor).  I do not want them to charge her as an accessory after the fact.  She threw away evidence.  That charge is not so far fetched.  And he needs to speak with the detective with an attorney.  And he needs to tell the truth as do you and your wife no matter the consequences.  Lies will catch up to all of you and the punishments MUCH harsher should they come to light later rather than sooner.