Their son is dead and they need to look for someone to blame. They, like most parents, are unwilling to face the prospect that the sweet little child they remember could possibly have had anything to do with his own demise.
even if this situation was exactly what they said it was....people are released on bail before trial all the time.
Welcome to the club!
The denial goes futher than their sweet little child. It is their OWN guilt for not being there for their child. Not setting limits. Not spending time with him, listening, helping him with the temptations of life.