How does his not coming forth with the information possibly protect them from criminal activity? If they were involved with known criminals, one would think the first thing JT or any other responsible person in authority would want would be the institutional power of the university getting involved and getting the proper authorities involved in order to remove those players from the activities and individuals in question--even if it came at the price of their ncaa eligibility. And if they were actually involved in the criminal activity, it would make his decision even worse and would cross over the line into obstruction of justice.
I haven't read anything to indicate the latter, but one poster did try to spin JT's actions in a positive manner as trying to protect his players from jail. With regards to just being around criminal activity, I don't believe that had anything to do with his decision, and if it did makes his actions worse not better.