Lawyer for American arrested by Russia on spying charges says he thinks he may be exchanged Paul Whelan was arrested in Moscow on Dec. 28 and accused of espionage.

Moscow -- The Russian lawyer of an American man arrested in Russia for alleged spying has raised the possibility his client will be convicted and exchanged for a Russian currently in jail in America.

The lawyer, Vladimir Zherebenkov, is representing Paul Whelan, the former Marine, who was arrested by Russia’s domestic intelligence agency on espionage charges last Friday.

Russia has not yet provided any details on the charges, which carry a possible jail sentence of 10 to 20 years. Whelan’s family have said it is impossible for him to be a spy and that he was wrongly arrested while attending a friend’s wedding in Moscow.

Speaking to ABC News on Thursday, Zherebenkov said Whelan intended to fight the charges and plead not guilty. But he then quickly brought up the possibility of an exchange, unprompted, and appeared to suggest he thought it was the most likely outcome. He also said he believed Whelan had been under surveillance by Russia's security services for "quite a long time."

"The thing is that in this category of cases, exchanges often happen," Zherebenkov said by telephone when asked what were the next stages in the case.

"For an exchange to happen, there has to be a court, the court has to examine the case, to prove his guilt, the sentence must come into legal force, after that the president can pardon him and an exchange can happen, for Russians citizens that are in detention in America," he said.

Asked if that meant he believed Whelan’s case would likely end with such an exchange, Zherebenkov said:

"It is not excluded-- such a practice exists. It exists and there are a lot of Russian citizens being held in America. Naturally, our state, our leadership are trying, by some means, to return them to the Motherland," he said.

He said that he expected the case would last at least 6 months to a year, after which an exchange might be possible.

"But I want to say that it is a long process — minimum half a year, longer even. As far long as all the evidence has not been examined and guilt is not fully established."

Neither Russia nor the United States as made any suggestion that an exchange is being considered, but the question of one has hung in the background because Whelan’s case follows closely on the heels of Maria Butina, a Russian gun rights activist who last month pleaded guilty in a U.S. court to acting as an illegal foreign agent. Butina admitted to trying to infiltrate American conservative political circles with the goal of influencing Republican policy towards Russia, acting on behalf of a well-connected Russian official.

Russia has denounced Butina's prosecution as a fabricated witch hunt and the two cases' proximity has quickly produced speculation around whether the arrest of Whelan might be retaliation by Russia’s government or that it might seek to make an exchange for her.

Asked if he had meant Butina when he had referred to an exchange, Zherebenkov said he did, but also listed two other convicted Russians currently held in U.S. jails and whose release the Russian government has repeatedly called for. He named Konstantin Yaroshenko, a pilot convicted of trying to smuggle $100 million worth of cocaine into America and Viktor Bout, an arms dealer suspected of working with Russian intelligence.

"I mean Butina, I mean Yaroshenko— that one worries me most of all, in that he is in a bad state of health -- and Bout is there, and also many other citizens, unfortunately," Zherebenkov said.

Zherebenkov, however, rejected the idea that Whelan’s arrest had any connection to Butina’s, saying that, as he understood it, Russia’s domestic security agency, the Federal Security Service or FSB, had been following Whelan long before her case.

"There is absolutely no connection," he said. "He fell into their field of vision, as far as I understand, earlier."

It is currently unclear though why Whelan would have attracted the eyes of the Russian security services. Russia has so far provided no details of what Whalen is accused of.

A native of Michigan, Whelan was a staff sergeant in the Marines who served two tours in Iraq in 2004 and 2006, service records show. But in 2008, he received a bad conduct discharge from the military and was demoted to the rank of private over larceny charges, according to the records.

Whelan is now the director of global security for BorgWarner Inc., a large American auto parts supplier, according to a statement from the company.

His family has expressed astonishment at his arrest and said the Russian charges cannot be true.

"He's got a military background, he's been in corporate security for years," Whelan's brother, David Whelan, said Tuesday. "He was going to be very well aware of the risks of traveling in Russia. I just don't see him putting himself in a position where he would be considered to break the law by a government like Russia's."

Dan Fried, the former top U.S. diplomat to Europe and now a distinguished fellow at the Atlantic Council, said some current U.S. officials see the arrest as a hostage-taking by Russia, comparing it to Andrew Bruson, the American pastor who was seized by Turkey and later released after lobbying by President Donald Trump.

Secretary of State Mike Pompeo was asked by reporters on Tuesday if he believed Russia had taken Whelan in retaliation for Butina's detention.

"We’ve made clear to the Russians our expectation that we will learn more about charges and come to understand what it is he is accused of and if the detention is not appropriate, we will demand his immediate release," Pompeo told reporters at a press conference in Brazil. On Thursday, the State Department declined to comment on the possibility of a swap after it was raised by Zherebenkov.

Zherebenkov said he has been acquainted with the charges against Whelan and some detailed case materials, but said he was not permitted to reveal them because of a non-disclosure agreement.

Zherebenkov said he expected an announcement that Whalen has been formerly charged to be made in the next two days and that they would contest them. He had filed on Thursday, he said, an appeal against Whelan’s pretrial detention, requesting he be released on bail.

Amid the silence from Russian officials, Rosbalt, a Russian news site known to have close ties to the security services ,published an article Wednesday containing what it claimed were the allegations against Whelan.

Rosbalt, citing an anonymous source in Russia's security services, alleged that Paul Whelan had been caught by FSB agents in possession of a memory card containing a classified list of secret Russian operatives.

On Thursday, Rosbalt published further allegations, asserting that Russia’s intelligence services believed Paul Whelan had worked as a spy for 10 years, seeking to recruit Russians picked by American intelligence agencies as promising sources with access to classified materials by befriending them on internet forums and then, years later, traveling to Russia to meet them.

Russian authorities have not commented on the Rosbalt reports and the claims have not been independently verified. The site is viewed by some experts as a place for sometime-targeted leaks from the security services and some interpreted them as a sign of what Whelan would be accused of, whether true or not.

Zherebenkov said he had read the Rosbalt reports but could not comment on them, citing the case's confidentiality agreement.

"As for if that will be confirmed, well, there will be an investigation, the criminal case will be investigated, and studied," the lawyer said, saying everything will be dealt with in court.

Despite that, he said he believed the Russian security services had been conducting surveillance on Whelan for a long time prior to his arrest.

"I suggest that surveillance was being conducted for quite a long time, they were observing his activity," Zherebenkov said, adding arrests in such cases only come after months of investigation. He did not elaborate on what activity he thought the Russians might have been observing.

A self-identified Russophile and avid traveler, Whalen has visited Russia previously. He has traveled to Moscow as a tourist and for work, according to his brother. Whelan has an account on the Russian social media site, VKontakte, which he appears to have used to mostly post holiday wishes and to express his condolences to Russians following disasters, sometimes in Russian.

Last week, he was in Russia to attend the wedding of an old friend from the Marines, who was marrying a Russian woman, his family said. He had been staying at the upscale Metropol hotel in central Moscow. On the day of Whelan's arrest, the group had gone sightseeing, touring the Kremlin. But his friends became alarmed when he did not appear for the ceremony a few hours later.

Whelan is now being held in Lefortovo prison, a former KGB detention center in Moscow, which is known for housing spies and other high value prisoners.

Zherebenkov, who visited Whelan on Wednesday, said he was in good spirits and that his rights were being observed.

"He feels entirely fine, he is holding himself with dignity, with confidence," Zherebenkov told ABC News. "Even with some humor."

Zherebenkov said Whalen was being held alone in a cell, but expected he would be placed with another inmate later, preferably an English-speaker, since his Russian is poor.

Whalen has been without a toothbrush, underwear or other essentials since his arrest, according to Zherebenkov, but the lawyer said he believed the prison would provide those Thursday. Whalen’s family will have to provide basic toiletries and clothes, as well as improved food, he said, which is standard practice in Russian detention centers.

Zherebenkov said that he was working off the basis that Whelan was innocent because Russia’s constitution guaranteed a presumption of innocence. But he said only a court and a full investigation could determine his guilt.

"I believe that we will, how to say, resist the investigation quite effectively, that is contest the charges and present evidence of his innocence," Zherebenkov said. "There is a lot of work to do."