(CNN) A Washington D.C. judge has thrown out a defamation case against a former British spy by three Russian oligarchs over a dossier alleging Russian interference in the 2016 US presidential elections.

Ex-MI6 officer Christopher Steele won the legal battle against billionaires Mikhail Fridman, Petr Aven and German Khan, who claimed he defamed them in the so-called dossier, which was published online in January 2017.

On Monday, Judge Anthony C. Epstein of the District of Columbia District Court upheld Steele's bid to have the case dismissed.

Epstein ruled that the plaintiffs failed to prove Steele was aware that some information in the dossier was incorrect or that he acted "with reckless disregard as to its falsity."

Steele's lawyers had argued that the case was an attempt to silence him. The Russians maintained he wasn't entitled to free speech protections because he is not an American citizen.

Writing in his judgment, Epstein said that "advocacy on issues of public interest has the capacity to inform public debate, and thereby furthers the purposes of the First Amendment, regardless of the citizenship or residency of the speakers."

The dossier was commissioned by Fusion GPS, a political research firm, as opposition research into then-candidate Donald Trump. Portions of the dossier remain unconfirmed.

Together, the three Russian men own stakes in Alfa Bank, the Russian bank the dossier claimed helped Russian operatives and Russian President Vladimir Putin influence the 2016 presidential election and other allegedly criminal acts. Alfa Bank denies this.

The trio have brought similar defamation cases against Fusion GPS and BuzzFeed, which published it online in January 2017, in New York state court and the federal court in DC.

President Trump has dismissed the Steele dossier on Twitter as "fake" and "fraudulent," and has called Steele a "lowlife." Trump has claimed that the document was paid for by his 2016 opponent former Secretary of State Hillary Clinton and the Democratic political party.