A former Marine was arrested in Russia on suspicion of spying. His family says he was just attending a wedding.

A former Marine who was arrested in Russia last week was simply attending a friend’s wedding, according to his family. Russian officials, however, maintain the American was on a spy mission.

Russia’s Federal Security Service (FSB) didn’t even acknowledge that Michigan resident Paul Whelan, 48, was in their custody until a few days ago, although he was detained on Dec. 28. His relatives learned of his detention from media reports.

U.S. consular officials requested access to Whelan on Monday — but were only granted access and spoke to him Wednesday, according to NPR. U.S. Ambassador to Russia John Huntsman was the one to visit Whelan, according to the State Department. Still, it’ll likely be a while before Whelan’s situation is sorted out and why he was arrested becomes clear, an anonymous government official told the Washington Post.

The U.S. government and Whelan should have been allowed consular access within 72 hours of the American citizen’s arrest, according to obligations outlined under the Vienna Convention, the Washington Post reported. It’s unclear whether the delay was a fault of Russia’s or caused by the U.S. partial government shutdown, since the State Department is operating with a smaller-than-normal staff.

Typically, consular officials provide a list of English-speaking attorneys and offer other local and U.S.-based resources, according to CNN. The details of talks between Whelan and the consulars, however, haven’t been released yet.

If convicted of espionage, Whelan could face up to 20 years in Russian jail.

Whelan’s twin brother, David, wrote on Twitter Tuesday that Whelan’s “innocence is undoubted, and we trust that his rights will be respected.”

Here’s everything we know so far:

Whelan, who has visited Russia several times, flew to Moscow on Dec. 22 for a fellow former Marine’s wedding, his family told CNN. The Michigan resident, who’s the director of global security for the automotive components supplier BorgWarner, was with the bride and groom at the Kremlin on Dec. 28 but didn’t show up to the wedding later that day. The couple quickly filed a missing persons report.

Since then, the FSB has released few other details and has only confirmed that officials arrested Whelan on suspicion of espionage.

"We've made clear to the Russians our expectation that we will learn more about the charges, come to understand what it is he's been accused of, and if the detention is not appropriate, we will demand his immediate return," U.S. Secretary of State Mike Pompeo told reporters during a trip to Brazil on Wednesday.

Whelan has been visiting Russia for business and personal reasons since at least 2007, according to the Washington Post. He was once a senior manager for the office staffing company Kelly Services. Whelan was a reservist in the Marines from 1994 until December 2008, when he received a bad-conduct discharge after being convicted on charges relating to larceny.

Whelan’s surprise arrest could be retaliation for the U.S. arrest of Maria Butina, the gun enthusiast and accused Russian political actor, former CIA officials told the Daily Beast. Russia could even be setting Butina up for a potential swap, the Washington Post reported. Butina, a former American University student, pleaded guilty to conspiring to act as a foreign agency last month. She’s been in jail since her arrest in July, when investigators alleged she maliciously became involved with the National Rifle Association and other conservative groups on behalf of the Russian government. She was accused of trying to develop some sort of “back channel” between Russian officials and some of the most influential political figures in the GOP.

Butina has since said she was acting “under direction of” a Russian official and agreed to broadly cooperate with investigators looking into Russian interference in U.S. politics in exchange for less prison time. Russian President Vladimir Putin, on the other hand, has insisted that Butina isn’t a spy and that Russian officials aren’t familiar with her.

Editor's note 1/2/19 4:00 p.m.: This story has been updated to reflect that U.S. Ambassador to Russia John Huntsman was the one to visit Whelan while he was detained.

Cover image: In this photo taken on Monday, July 16, 2018, Russian President Vladimir Putin gestures while speaking at the joint press conference with U.S. President Donald Trump after their meeting at the Presidential Palace in Helsinki, Finland. (AP Photo/Alexander Zemlianichenko)