Well, you are right that there is no canonical crime for cover up if there is no state law requiring reporting.  It appears from the letter written to the bishops that there is such a law in the jurisdiction where the offense occurred.  Whether or not the accused priest, the bishop, the other priest helping his friend, and the nuns abridged the civil law is a matter for the civil legal system to work out.  And, if I understand how the Vatican operates, they will wait for the civil law to "do its thing" before then dealing any connection to canonical law.  

It bothers me that Francis seems frozen, unable to act at all, in the face of the stupidity, the cruelty, the actual creation of a scandal caused by this case.  He looks like the servant of the civil world when he just waits, doing nothing, saying nothing.  God, morality, kindness and succor for the afflicted, accountability of those complicit to the institution, accountability of the institution to the victim, all comes second.