Article 24, paragraphs 8-10?
It looks like you would have to file a criminal complaint in order to proceed with a civil claim, and the state cannot act on criminal charges until you actually make the complaint, unless the defamation appeared in the mass media. If the Finnish prosecutor declines to act against the FBI, your only remaining remedy is to file a claim in the court of public opinion by getting a local journalist to tell your story on a slow news day.
You owe it to yourself and all noncriminal Finnish hackers to at least make a defamation complaint to Finnish police against the FBI. Your statute of limitations is 5 years.