Russia detained an American for espionage. Here’s what we know.

Paul Whelan, a former Marine and businessman, was arrested over the weekend while attending a wedding in Moscow.

Russian authorities detained an American citizen in Moscow last week on allegations of espionage, a curious move that could worsen already tense relations between the US and Russia.

Paul Whelan, a 48-year-old former Marine, was reportedly in Moscow to attend a wedding when he was arrested on December 28. Russia’s domestic security services (FSB) said Whelan was apprehended while on a “spy mission,” but did not elaborate on the charges against him.

A State Department spokesperson confirmed to Vox Wednesday that US Ambassador Jon Huntsman visited Whelan at a Russian detention facility, but didn’t offer any other details due to privacy concerns. The spokesperson added that Huntsman had been in touch with Whelan’s family.

Secretary of State Mike Pompeo briefly addressed Whelan’s detention during a trip to Brazil. “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,” Pompeo told reporters Wednesday.

Whelan’s family members, for their part, have dismissed allegations of espionage. In a statement, they said Whelan’s “innocence is undoubted.”

Whelan’s detainment comes about two weeks after 30-year-old Russian national Maria Butina, who was arrested on charges of conspiracy and acting as an agent of a foreign government in July 2018, admitted to participating in a campaign backed by Russian officials to secretly influence US politics, including trying to sway the Republican Party to be more receptive to Russia. Some experts have speculated that Whelan’s arrest may be an attempt by Russian President Vladimir Putin to retaliate.

Whelan could face up to 20 years in prison if convicted for spying. But the details of his arrest, and Russia’s motivations or justification for detaining him, are still unclear. Here’s what we know so far.

Who is Paul Whelan?

Paul Whelan’s family describes him as a former Marine and former law enforcement officer from Michigan, and a kind and loyal person who had an interest in Russia and Russian culture. The Kremlin claims the American was a spy — but so far has offered no real evidence to back up its explosive allegations.

Whelan served in the Marine Corps Reserve from 1994 to 2008 and, according to the Wall Street Journal, was deployed twice to Iraq, though he didn’t see combat. Whelan was discharged in 2008 for bad conduct, after being court-martialed on charges of larceny. The details of the case are not clear.

Whelan currently works as the director of global security for BorgWarner Inc., a Detroit-based auto parts supplier, according to his family and the company. “He was not on company business, it is our understanding he was on a personal trip,” Kathy Graham, a spokesperson for BorgWarner, told the New York Times. “We do not have any facilities in Russia.”

Whelan’s family said he flew to Moscow on December 22 with plans to attend the wedding of a fellow former Marine. David Whelan, Paul’s twin brother, told CNN that when his brother didn’t show up for the Saturday wedding, the couple filed a missing persons report. It wasn’t until Monday that Whelan’s family confirmed he had been detained by Russian authorities.

But this wasn’t Whelan’s first trip to Russia. A Marine Corps publication dated November 2006 (h/t Quartz) printed a photo of Whelan in front of St. Basil’s Cathedral in Moscow’s Red Square, with a caption that said he was spending “two weeks of rest and recuperation leave in Moscow.”

On his personal website, Whelan wrote after that trip that it had been a “dream” to visit Russia. “I was fortunate enough to meet nice people and had several pleasant excursions throughout the country,” he wrote, according to the Daily Beast.

The Washington Post interviewed several of Whelan’s acquaintances in Russia, who described him as “a friendly man who greatly appreciated Russia,” with a basic command of the language.

Whelan’s brother David also told the Wall Street Journal that Whelan, having traveled to Russia before, was aware of the risks. Whelan, he said, “would not have knowingly broken any law, let alone one involving espionage.”

Was Whelan’s detainment revenge for Maria Butina?

US Ambassador Huntsman met with Whelan on Wednesday, five days after his arrest. But the details of why Russia thinks Whelan is a spy are still frustratingly unclear.

The timing of Whelan’s detention is certainly notable. A little more than two weeks ago, Russian citizen Maria Butina admitted that she tried to influence US politics by infiltrating Republican political circles and conservative-leaning interest groups — most notably the National Rifle Association. Butina was arrested in July but reached a deal with federal prosecutors in December and pleaded guilty to one count of conspiring to act as a foreign agent.

After Butina’s arrest in July, the Russian foreign ministry started a campaign in support of the Russian citizen — complete with the hashtag #FreeMariaButina. Putin previously claimed that he hadn’t heard of Butina until her arrest in the US and denied she had any ties to Russian spies.

At a speech and press conference on December 20, though, the Russian president went further, claiming that the charges against Butina were concocted and that she pleaded guilty only under threat of a lengthy prison sentence. “I don’t understand what she could have pleaded guilty to because she was not there to fulfill any government tasks,” Putin said.

“We will see how it plays out,” he added. “We do care, and we will keep an eye on this case and provide our support accordingly.”

Putin’s apparent ire over Butina’s arrest has led some to speculate that Whelan’s detention is a form of retaliation — not an unusual move for the Kremlin. “Russia has a history of tit-for-tat diplomatic expulsions, and so forth, when there’s any kind of a spy case,” Kimberly Marten, a Russia expert and political science professor at Barnard College, Columbia University told me.

Marten added that Putin’s remarks about Butina in his December address also indicate that Whelan’s arrest could be a form of payback. But, she cautioned, “we don’t really know enough yet to say for sure.”

But other Russia watchers have expressed similar concerns. Former US Ambassador to Russia Michael McFaul called the situation strange on Tuesday and demanded Russia provide an explanation. Bill Browder, a longtime critic of Putin whose lobbying of Congress led to the passage of the Magnitsky Rule of Law Accountability Act in 2012, called Whelan’s detention “a hostage situation.”

Experts have also noted that it’s pretty rare for Russia to detain a private US citizen, and that Whelan’s background doesn’t exactly scream spy.

“The one thing I can say for certain,” John Sipher, a former member of the CIA’s Clandestine Service, told NPR, “is this is not how the US commits espionage overseas. We would never put a US citizen, without diplomatic immunity, in harm’s way this way, especially looking after low-level things like this.”

At a press conference in Brazil on Wednesday, Secretary of State Pompeo said the US would demand Whelan’s release if his detention was inappropriate, but the Trump administration has otherwise been pretty quiet about the arrest.

That’s a bit surprising since President Donald Trump has personally taken up the causes of Americans who were being held abroad in the past. He had success in returning American hostages where other presidents have failed, including Pastor Andrew Brunson, who’d been imprisoned in Turkey since 2016, and multiple Americans detained in North Korea. (As of publication time, the White House had not responded to Vox’s request for comment.)

Whelan’s arrest also comes as relations between Russia and the US are under strain. There’s continuing Russian aggression in Ukraine. The US is still grappling with Russia’s interference in the 2016 elections, and there’s evidence the Kremlin continued to meddle in the 2018 midterm elections.

In his December 20 speech, Putin warned of the risk of nuclear war because of the US’s decision to abandon Cold War-era weapons treaties. The US has given Moscow until February to comply with the Intermediate-Range Nuclear Forces (INF) Treaty, and some experts think a breach could potentially jump-start an arms race.

Whelan’s arrest and status remain mostly a mystery, for now. Plenty of questions remain about Putin’s endgame, and whether this will exacerbate tensions between the US and Russia.