It’s called “accessory after the fact”, and they wouldn’t be guilty of it if they report it, that’s the whole point of reporting it.

An accessory must generally have knowledge that a crime is being committed, will be committed, or has been committed. A person with such knowledge may become an accessory by helping or encouraging the criminal in some way. The assistance to the criminal may be of any type, including emotional or financial assistance as well as physical assistance or concealment.