It seems standard operating procedure for the Justice system to blackmail people with the threat of charges or long sentences to get them to say what they want them to say.
First Amendment jurisprudence has established that news organizations cannot be prosecuted just because they publish materials that may have been obtained illegally — as long as they were not involved in the unlawful process of obtaining them.
The key point of contention in the investigation may turn out to be whether Project Veritas was involved in instigating the theft of the diary, or if it simply obtained the diary independently of the process through which it was unlawfully obtained.