For the second time in three years, U.S. Attorneys have sought to prosecute foreign nationals at NASA on national security grounds, only to dramatically reverse course and shut down their investigations.

Most recently, federal prosecutors abruptly ended their case on May 3 against Bo Jiang, a Chinese citizen and former NASA contractor at the agency's Langley Research Center.

Jiang had been arrested March 16 when federal agents intercepted him at Dulles International Airport as he tried to board a one-way flight for China. He was carrying two laptops and associated equipment.

But in the end, the authorities accepted a plea agreement in which Jiang pleaded guilty to one count of violating a NASA equipment regulation and agreed to leave the country within 48 hours.

Jiang's case bears striking similarities to one at NASA's Ames Research Center. There, British national Will Marshall was reportedly intercepted by federal agents in June 2009 at San Francisco's International Airport. He was carrying a government-issued laptop.

Congressional leaders claim they've been told by NASA whistleblowers that the White House and the Justice Department interfered with the Ames investigation and removed prosecutor Gary Frye, the Assistant U.S. Attorney who was originally in charge of the case.

Sen. Charles Grassley, R-Iowa, the ranking Republican on the Senate Judiciary Committee, sent a February letter to the U.S. Assistant Attorney General Lisa O. Monaco asking if "political considerations" influenced the decision not to prosecute Marshall.

Two House appropriations subcommittee chairmen with jurisdiction over Justice Department and NASA spending also signed the letter.

The U.S. Attorneys office for the Eastern District of Virginia, which handled the Jiang case, declined to comment about Washington involvement in the Jiang case.

Originally, the federal prosecutors heralded the Jiang case as a potential spy case.

Neil H. MacBride, U.S. Attorney for the Eastern District of Virginia, headed the case, with assistance from Justice Department Counterespionage Section attorney A. William Mackie.

Jiang carried a NASA laptop to China last year containing sensitive and proprietary, although not classified, information, according to federal sources. The information originally from NASA scientist Zia ur-Rahman contained operational source coding for aviation imaging.

Just before his arrest, Jiang was terminated as a NASA Langley contract employee for taking Rahman's work to China, a NASA security violation. He was forced to surrender his government-issued laptop and barred from entering NASA grounds.

The Chinese national moved up his airline reservation by two weeks after The Washington Examiner named him in an article about NASA Langley, according to court filings by the U.S. Attorneys office.

On March 16, agents from the FBI and the U.S. Department of Homeland Security arrested Jiang as he attempted to board a flight to China with a one-way ticket.

An FBI affidavit at the time tied Jiang to "substantive violations" of the Arms Export Control Act, which bars foreign nationals from gaining access to classified defense-related information.

Until the last moment, the U.S. Attorneys office promised an aggressive prosecution against the Chinese citizen. Government filings cite Jiang as a "flight risk" who had violated NASA security regulations, deceived federal agents and gave them fraudulent information.

On May 3, the U.S. Attorneys office reversed itself and signed a plea agreement with Jiang dropping all felony charges except for a misdemeanor charge.

Although national security was originally the heart of the case, the government said Jiang was guilty only of illegally downloading movies and "sexually explicit" material on his NASA-issued laptop.

"In effect, he was convicted of having a little porn," complains Fernando Groene, Jiang's court-appointed attorney in an interview with The Washington Examiner.

The government ordered Jiang to leave the United States within 48 hours. Although Jiang was on "supervised release," the FBI told The Washington Examiner that agents did not escort him to Dulles International Airport.

Vanessa Torres, an FBI spokesman also erroneously said Jiang had booked a China Airways flight. In fact, Groene said Jiang took a United Airlines flight to Beijing.

In the Ames case, congressional sources claim Frye, the Assistant U.S. Attorney in San Francisco was initially assigned the NASA Ames case, but was abruptly removed.

In a February 27 letter to U.S. Attorney Melinda Haag, Grassley, Rep. Frank Wolf, R-VA, and Rep. Lamar Smith, R-TX, asked why Frye was removed and a government witness was cancelled before the grand jury in February 2011.

Wolf is chairman of a House appropriations subcommittee that oversees NASA and the Justice Department. Smith is chairman of the Science, Space and Technology Committee.

The three lawmakers told Haag they were concerned "politics played a role in the prosecutorial decisions made in this case."

Haag has said that she never requested authority to prosecute anyone on espionage and that the "allegations are untrue" that her office sought Justice Department authority to bring charges against officials at NASA Ames.

The congressmen have yet to receive a direct response from either Haag or Monaco. However, The Washington Examiner obtained an April 17, 2013, letter from Peter Kadzik, head of the Justice Department's office of legislative affairs, to the three lawmakers.

Kadzik said only that the Department "will respond further at a later date" concerning possible political interference in NASA Ames case. But then he asked "whether your law enforcement sources would be willing to speak with us."

NASA whistleblowers contacted by The Washington Examiner say they do not trust the Justice Department. Two said they fear retaliation by an administration they regard as hostile to career employees who don't tow the accepted political line.

On March 20, NASA Administrator Charles Bolden agreed to restrict access to foreign nationals, informing Wolf's subcommittee that "I've ordered a complete review of the access that foreign nationals are granted at NASA facilities."

Groene says he believes Jiang's release by federal authorities "exonerates" his client. But, he laments, the possibility of working in the U.S. again "is very limited to non-existent."

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Richard Pollock is a member of The Washington Examiner Watchdog investigative reporting team. He can be reached at