That's exactly what I believe: there are files there that will incriminate him in committing those acts himself. I find it hard to argue he should be left alone, but I suppose that's just a gut reaction?
Probability isn't sufficient, in this philosophy, because it's a trap. Of course probably he has on these drives what prosecutors claim, or worse, evidence of his direct involvement. And the trap is the injection of lack of sympathy into the decision making process; of course any reasonable person will say, eww he's almost certainly a creep therefore I'm not sympathetic to his indefinite incarceration. But that's exactly what the philosophy was supposedly designed to avoid, any possibility that innocent people get jailed; not preventing guilty people going free.
This is why you see a lot of effort by prosecutors defending against introduction of new evidence to prove innocence; because proving innocence well after a guilty verdict, itself shows the possibility of jailing innocents. It taints the system. And then you get these ever more perverse notions that executing those who later prove themselves innocent is not an unconstitutional execution when that person had received a free and fair trial finding them guilty of a capital crime. http://www.businessinsider.com/antonin-scalia-says-executing...
As I said earlier I am not taking a position on whether what he did was right or wrong or on the moral aspects of the subject matter but here in the US the government must have a warrant to search electronic devices and that warrant must name the material they are seeking. If they list images related to child pornography, child molestation, etc they cannot go looking for evidence of drug dealing per se. But let's assume they find evidence of drug dealing, do you not think they will simply broaden the scope of their investigation and go looking in every corner of s life to now prove something they previously were unaware of before they hypothetically gain access to the drive.