There is no blanket provision to make unlawfully obtained evidence inadmissible but the judge must still forbid using any document that was i.a. obtained through a "gross" violation of the person's legal rights. So in this specific case the evidence would probably be inadmissible.
But a violation by the police, not necessarily a violation by a third party.
There was a case in France where the suspect of a murder case fled to Germany which refused to extradite him. The father of the victim organised a kidnapping and left the guy attached in front of a French police station. The father was prosecuted for kidnapping, but that didn't help the alleged murderer who was then arrested and charged.
I don't know what the law is in Finland, but usually medical secrecy only covers specific stuff, and likely not the admission of a crime, unlike attorney-client privilege (which is specifically designed to cover crimes committed).
The relevant part here is probably the last paragraph of section 25. It concerns the rules for admitting evidence that has not been given by the person themselves in an official investigation, and which has been obtained unlawfully. It is on page 97 in the linked PDF:
> [...] the court may use also evidence that has been obtained unlawfully unless such use would:
> * endanger the conduct of fair proceedings
> * taking into consideration the nature of the matter, the seriousness of the violation of law in obtaining the evidence
> * the significance of the method of obtaining the evidence in relation to its credibility
> * the significance of the evidence for deciding the matter
> * and the other circumstances.
Namely, considering that these documents were obtained in probably the most heinous possible violation of the person's privacy, it would not be possible for the court to admit them as evidence. That's anyway completely moot, as if it ever became publicly known that a prosecutor or police officer had read any of these documents it would be very scandalous in of itself.
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.
in the US, the govt can't use illegal means to obtain documents, but if a criminal's information is exposed by another criminal, it's available to be used.
