If they suspect you of operating a child porn ring, they know that you will most likely take precaution and nuke everything if you even catch wind that you are

If they suspect you of operating a child porn ring, they know that you will most likely take precaution and nuke everything if you even catch wind that you are under investigation, which is why they will subpoena your bank records, phone records, ISP records, and probably put surveillance on you. If the only thing that shows up from all the data is literally a public DNS that points to a public ip address with questionable content, while you are leading a relatively normal life with all your other income accounted for, the agency (given that they have enough tech experience in cybercrime here) will most likely assume that you are a victim, and will go talk to you. Now of course, nothing is for certain, but statistically speaking, FBI doesn't go busting doors without prior investigation.