A federal judge referred the lawyers behind the Prenda Law "copyright trolling" scheme to investigators in 2013. Since then, there's been no indication of what stage an investigation is at, or if it's happening at all.

Now, two co-founders of The Pirate Bay have said they have reason to believe that an investigation is underway. Peter Sunde and Fredrik Neij each independently told the website TorrentFreak that Swedish authorities questioned them during their recent imprisonment.

The Prenda Law strategy was to sue large numbers of Internet users for downloading pornography and then settle fast for several thousand dollars. The scheme netted millions over the years, but it was shut down in 2013 after sanctions from US District Judge Otis Wright. Other judges have punished Prenda since then. The harsh results were appealed, but to no avail.

One of the more serious allegations against Prenda was that the pirated material had actually been planted on The Pirate Bay as a kind of "honeypot." The honeypot theory would obliterate any right to enforce copyright, since they had initiated the sharing. Prenda wasn't protecting other people's pornography—the copyright troll had essentially become its own client.

The Pirate Bay provided records they believed showed the honeypot theory was true, and that's what the police questioning was about. An expert hired by defense lawyers connected a Pirate Bay account called "sharkmp4" to Prenda mastermind John Steele, but Steele denied involvement.

The Pirate Bay founders' statements published today suggest that it's a trail the FBI is trying to re-trace.

"I was told that Prenda Law has been under investigation for over a year, and from the printouts they showed me, I believe that," Sunde told TorrentFreak. "They asked many questions about the TPB backups and logs. I told them that even if they have one of the backups that it would be nearly impossible to decrypt."

“They wanted to know if I could verify the accuracy of the IP-address logs, how they were stored, and how they could be retrieved,” Neij added.

Neither Neij and Sunde could help with the request, since they no longer run the site. The officers also asked about just who is running the Pirate Bay these days, so it's not clear what the real motive of the questioning was. Both men were interviewed by Swedish police, but the Swedish officers said they were "sent on behalf of the FBI."

Neij flouted a Swedish arrest warrant but was arrested near the Thai-Laos border in 2014. He served two-thirds of a 10-month prison term and was released last month. Sunde was arrested last year as well and spent five months in prison.