On Monday, Russian prosecutors asked that Paul Whelan, a former US Marine, be sentenced to 18 years in prison for spying.
Mr Whelan claims he was set up in a sting operation, and has pleaded not guilty to the charges.
Russian prosecutors claim Mr Whelan obtained state secrets. Mr Whelan claims that while he did accept a USB drive, he believed the drive contained holiday photos, not Russian state secrets.
At the time of his arrest, Mr Whelan was the director of global security for auto parts supplier BorgWarner. He previously spent 14 years in the US Marine Corps and was discharged for bad conduct in 2008. Mr Whelan claimed he was visiting Russia to attend a wedding at the time of the arrest.
Mr Whelan's lawyer, Vladimir Zherebenkov, said the court's decision was expected on 15 June. Another member of his defence team, Olga Karlova, described his closing statements.
"In his moving closing remarks, he spoke about how much he loves Russia and Russian people, and he never wished them ill," she said.
The trial began on 23 March and was closed to the public due to the discussion of classified information.
Reuters reported that US authorities are calling the charges against Mr Whelan "spurious" and have demanded he be released. According to the Moscow Times, there is speculation in Moscow that the US and Russia will participate in a prisoner exchange to arrange the return of Mr Whelan.
"This secret trial is a mockery of justice," John Sullivan, the US ambassador to Russia, said. "There is no legitimacy to a procedure that is hidden behind closed doors. It is not transparent, it is not fair, and it is not impartial."
Speaking to CBS News, Mr Whelan's twin brother, David, said he believed the charges were without evidence, but nonetheless did not expect an acquittal. His sister, Elizabeth, tweeted "There was no crime. This is political hostage-taking."
"We expect a wrongful conviction and can only hope that the sentence is at the lighter end of the range," he said.
Mr Whelan claims he's been mistreated by the Russian guards and denied needed medical attention. His guards, however, claim he's faking his health problems to try to garner sympathy for his case.