President-elect Donald Trump's nominee for national security adviser partnered in recent months with a technology company co-led by a businessman who pleaded guilty to trying to sell stolen scientific material in the 1980s to the KGB, the former Soviet intelligence service.

Retired Lt. Gen. Michael Flynn joined the advisory board of Brainwave Science in February, company documents show. The Massachusetts firm develops controversial "brain fingerprinting" technology designed to assess whether people under interrogation are being truthful by measuring their brain waves. The firm offers training in how to use the technology, in partnership with Flynn's consulting firm, Flynn Intel Group, according to Brainwave's website.

One of Brainwave's two-member board of directors was Sabu Kota, an Indian-born software engineer who pleaded guilty in 1996 to selling stolen biotech material to an FBI agent posing as a Soviet spy. Prosecutors said the sale stemmed from what they called Kota's involvement in a spy ring that passed sensitive defense technology to the KGB between 1985 and 1990, according to a Defense Department summary of the case.

Brainwave Science removed Kota's name from the company website sometime between Thursday and Friday, when Bloomberg News published a report about Flynn's ties to the firm, according to a search of archived Google data. Company officials and officials from Trump's transition team did not respond to requests for comment on Friday, and Kota did not respond to messages left at his home.

Kota's lawyer denied that he had any connection to spying when he was charged in 1995, and Kota told Bloomberg that the criminal charges were a misunderstanding and stemmed from a patent dispute, not espionage.

Bloomberg also quoted a Trump transition official as saying that Flynn had no dealings with Kota during his time working with Brainwave and that he has ended his association with the firm.

The connection between Flynn - a decorated military intelligence officer and former head of the Defense Intelligence Agency - and the company is the latest controversy involving relations between Russia and Trump or members of his team. Trump has faced criticism for expressing his admiration for Russian President Vladimir Putin, and on Friday the president-elect released what he called "a very nice letter" from the Russian leader.

Flynn stunned former colleagues when he traveled to Moscow last year to appear alongside Putin at a lavish gala for the state-run channel RT, a trip Flynn admitted he was paid to make. Former U.S. officials said Flynn, seen dining next to Putin in photos published by Russian outlets, was used as a prop by the autocratic leader.

Flynn defended the trip, saying he saw no distinction between RT and U.S. news channels such as CNN, and that he had pressed Putin's government to behave more responsibly in international affairs.

The length and precise nature of Flynn's contacts with the Brainwave firm could not be determined on Friday. Bloomberg reported that Flynn was supposed to help drum up new business for the firm with U.S. agencies, and that he has met with company officials at least 10 times. The meetings reportedly were held as late as September, when Flynn helped pitch Brainwave's services to officials from the Bangladeshi defense forces.

Independent scientists have disputed the accuracy and reliability of brain fingerprinting, and Brainwave has not released research supporting its claims that the tool is highly effective.

But Bloomberg quoted Brainwave President Krishna Ika as saying that Flynn had tested the device himself, donning a helmet-like headpiece fitted with sensors. "He found it very convincing," Ika told the news service.

Julie Tate and Laura Helmuth contributed to this report.