This was my thinking as well. The overwhelming majority of cases you hear about are broken using old-fashioned police work. Even petitioning ISPs for records seems to be a fairly minor part of the equation.
A pedophile running a hidden TrueCrypt volume and using Tor to trade chid pornography on onion sites is likely to get caught only if they pull a Bradley Manning, that is, saying the wrong thing to the wrong person. Unfortunately, most pedophiles these days that trade in child porn are likely more technologically advanced than the people responsible for tracking them.
A pedophile running a hidden TrueCrypt volume and using Tor to trade chid pornography on onion sites is likely to get caught only if they pull a Bradley Manning, that is, saying the wrong thing to the wrong person. Unfortunately, most pedophiles these days that trade in child porn are likely more technologically advanced than the people responsible for tracking them.