This seems a clear and valid conviction.

An accessory is a person who assists in the commission of a crime, but who does not actually participate in the commission of the crime as a joint principal. The distinction between an accessory and a principal is a question of fact and degree:- http://en.wikipedia.org/wiki/Accessory_%28legal_term%29

Accessory after the fact - Someone who assists another 1) who has committed a felony, 2) after the person has committed the felony, 3) with knowledge that the person committed the felony, and 4) with the intent to help the person avoid arrest or punishment. An accessory after the fact may be held liable for, inter alia, obstruction of justice. - http://www.law.cornell.edu/wex/accessory_after_the_fact

It is a moot point in the case of repeat offenders, as to which category of accessory the cover-up facilitators were.

Any evidence implicating others, should be considered for further prosecutions.