There's plenty that can be done that never involves having to look at an image yourself.
For instance, if I gave you a specific file name/size/hash (but not showing you the actual image), could you find out who possesses it, is distributing it, and anything about their location or identity that would aid law enforcement in catching the bandit?
I strongly suspect that anti-CP laws have an exemption for people engaged in law enforcement and the judicial system engaged in real investigations. Otherwise it would be impossible for anyone to be prosecuted for CP. The law makers aren't thad silly.
You are correct. Law enforcement involved in these investigations absolutely looks at CP. If they confiscate a computer with 10,000 CP images, they're looking at every one, day in and day out, and putting together a case for the prosecution. I'm glad that's not my job, and thankful for those whose it is.
I don't know much about US law, but in my country it's illegal to even look at an image, even if it is part of a private investigation.
I'm sure that many would volunteer to help, but not while they'd risk jail time themselves