The case is Schrader v. District Attorney, decided yesterday by the Third Circuit (in an opinion by Judge Stephanos Bibas, joined by Judges Patty Shwartz and Julio Fuentes). First, what I think is the heart of the First Amendment argument:
The DA could have gotten a protective order stopping Bowie from sharing the discovery documents before he did so. Instead, the DA got a protective order only after Bowie had shared them. When "the government has failed to police itself in disseminating information," prosecuting someone who later publishes that information "can hardly be said to be a narrowly tailored means of safeguarding" confidentiality.
And now a longer excerpt: