Most likely these documents are protected from prosecutors in the same way they would be without the breach, because the breach does not alter the type of document.
It's not all black & white. In the ANOM case the FBI, through a Swiss cover company, sold criminals "super encrypted" mobile phones.[1] In reality, the phones were backdoored and all their messaging leaked to the FBI. This uncovered several criminal operations in Finland such as drug trafficking rings. The FBI shared this correspondence with the Finnish police.
When the case came to court, the defendants' first action was of course asking the court to suppress all evidence from the FBI because it was obtained illegally, as the criminals obviously had an expectation to the privacy of their correspondence, which was illegally violated. The court actually ruled that the messages are only admissible if they pertain to crimes that carry a maximum penalty of at least four years in prison, which is the same threshold that allows the Finnish law enforcement to use wiretapping.[2]
Communications between a client and a professional (physician, lawyer etc.) generally have specific protections carved out in the criminal procedure of most countries and can't be compared to a random chat app.
