Russian interference in the U.S. presidential elections is at the heart of a secretive treason case against a former FSB official and three of his alleged accomplices arrested last year, a Russian news startup reports.

Sergei Mikhailov, the FSB’s former head of cyber investigations, was detained on Dec. 5, 2016, together with three alleged accomplices — his colleague Dmitry Dokuchayev, former Kaspersky Lab employee Ruslan Stoyanov, and internet entrepreneur Georgy Fomchenkov.

The four men have been held in Moscow’s high-security Lefortovo Prison on charges of committing treason. The mysterious case has been hidden from public view after being labeled a “state secret.”

“The four men have been hidden away from everyone, to make sure they don’t give away any sensitive information,” the Bell outlet cited Ivan Pavlov, a lawyer for one of the defendants, as saying.

In an extensive investigation published on the one-year anniversary of the group's arrest, the Bell outlet cited two unidentified sources who said the move to arrest the men was ordered by the Russian military intelligence, the General Staff of the Armed Forces (GRU), in an internal power struggle over state funding.

An earlier report by Crowdstrike, a cybersecurity firm hired by the Democratic National Committee (DNC) to look into alleged Russian election meddling, said Hillary Clinton’s campaign and the DNC had been targeted by Russian hackers on two separate occasions.

The first attack, allegedly carried out by the FSB, went unnoticed until a second was carried out by the GRU — with the two agencies seemingly working independently of each other.