If a kilo of heroin just showed up in the back seat of my car, I'd throw it out the window and try not to think about it. I certainly wouldn't bring it to the police, because mere possession is a serious crime.

CP is the same way, except it comes with a nice audit trail which could sink me even if I delete it immediately. Do I risk that, or do I risk the FBI deciding I'm a Person of Interest because I reported the incident in good faith?

There are no good choices there.

And that includes the FBI.