Last May, Dr. Xiaoxing Xi awoke to find a team of FBI agents brandishing guns and screaming at him to put his hands behind his back. Agents slammed the 57-year-old Temple University physics professor against a wall and dragged him away in handcuffs — all in front of his wife and two daughters.

The FBI accused Xi — a naturalized US citizen — of passing along sensitive information to China. Just four months later, the federal government's case fell apart. All charges were dropped, but the damage was already done.

"I don't think my wife has had a single night of good sleep since that day," Xi said, referencing the early morning FBI raid. "My reputation was damaged and I almost lost my job."

Xi's case is just one of several high-profile espionage investigations targeting Asian-American scientists that the FBI has bungled in recent years.

Last October, the FBI arrested Sherry Chen, a hydrologist with the US National Weather Service in Ohio, and accused her of stealing passwords to download information about America's dams. Chen was handcuffed at work and threatened with 25 years in prison. She was suspended from her job, and had to ask relatives in China to help pay for her legal defense. Five months later, the case against her collapsed for lack of evidence. It turned out all she did was email publicly available information to a friend in China.

In December 2014, the FBI dropped charges against two other Chinese American researchers, Guoqing Cao and Shuyu Li, who were accused of passing sensitive pharmaceutical information to a Chinese company.

Chris Kang, president of the National Council of Asian Pacific Americans (NCAPA), said the FBI has arrested and later released five Asian-American scientists in the last year alone. "I don't know if it's a series of good faith mistakes or not," Kang said. "But at the very least, we are seeing a pattern of disturbing behavior."

'There's two things that are happening: Either it's a stunning lack of competence, or there's a racial profiling going on.'

After the DOJ dropped charges against Chen last March, Congressman Ted Lieu, a Democrat from California, and member of the Congressional Asian Pacific American Caucus, wrote Attorney General Loretta Lynch and demanded to know if Chen had been targeted because she was Asian. The DOJ told Lieu that wasn't the case.

Just two months later, the same thing happened to Xi. "You just cannot have this pattern of multiple cases of Americans being arrested and indicted for espionage," Lieu told VICE News. "These people are being falsely accused, it's wrecking lives, and they all just happen to be Asian-American."

Xi's case, Lieu said, illustrates how the FBI is punishing Asian-American scientists for common research practices. Xi is one of the leading experts on magnesium diboride (MgB2), a compound that can serve as a superconductor, and has some potential applications in explosives and airplane technology. The FBI broke into Xi's house that morning because they believed Xi had been passing along the schematics of a device that produces MgB2, known as a "pocket heater," to entities in China.

But he did no such thing. Almost immediately after Xi's arrest, a swarm of superconductor experts rushed to his defense. Expert testimony quickly proved that the communications the FBI built their case upon showed Xi engaged in normal academic correspondence with colleagues in China.

"I don't expect them to understand everything I do," Xi told the New York Times. "But the fact that they don't consult with experts and then charge me? Put my family through all this? Damage my reputation? They shouldn't do this. This is not a joke. This is not a game."

Of course, not every case of espionage involving an Asian-American has fallen apart. In 2010, Boeing engineer Dongfan Chung was sentenced to 16 years in prison for passing details of the US space program to China. But the recent blunders by the FBI has led Asian-American groups and their allies in Congress to demand answers from the Obama administration.

Shortly after the charges against Xi were dropped, Lieu wrote another aggrieved letter to the attorney general, and convinced 44 other members of Congress to sign on. Lieu noted "a pattern and practice of minorities being singled out," and demanded that the DOJ explain itself and conduct an internal investigation.

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The Asian-American Bar Association also stepped in, writing its own letter to Lynch that noted "a pattern of treatment of Americans whose civil rights and civil liberties are being impinged upon because of their national origin or ethnic heritage without full support of the facts."

On Tuesday, the NCAPA and the Congressional Asian Pacific American Caucus accused the DOJ of racial profiling during a press conference attended by Xi and Sherry Chen. "[There] appears to be a practice and pattern of the federal government profiling Chinese Americans as spies," Congresswoman Judy Chu, the chair of the caucus, said while standing beside Chen and Xi. Chen choked back tears, and Xi looked to be on the brink of breaking down.

"We cannot tolerate another case of Asian-Americans being wrongfully suspected of espionage," Chu said. "The profiling must end."

Later that day, Chu grilled the attorney general at a House Oversight Committee hearing, and demanded to know why the FBI kept going after Asian-American scientists. She asked for specific answers on the Xi and Chen cases. Chu had invited both scientists to attend the hearing, and they sat directly behind Lynch as she declined to offer up any details.

"The FBI does not focus an investigation on any individual on the basis of their race and their national origin," Lynch told Chu. "With respect to those specific cases, I am not able to comment at this time."

Congressman Ted Lieu is running out of patience. "There's two things that are happening: Either it's a stunning lack of competence, or there's a racial profiling going on," he told VICE News. "I do not have any indication they are taking this pattern very seriously."

The DOJ did not respond to repeated requests from VICE News to comment. On Wednesday, Lynch met behind closed doors with concerned members of Congress who pressed her on the racial profiling question.

Chu attended the meeting, and her office told VICE News that it was a "frank and serious conversation." But so far, the Justice Department has not admitted that race or ethnicity played into its arrests of Asian-American researchers. And it has not responded publicly to calls for an independent investigation.

"Until then, employees that look like me are going to keep getting indicted at higher rates," Lieu said. "And I do not want to read about any more Sherry Chens or Professor Xis."

Meanwhile, NCAPA is sounding the alarm in Asian-American communities across the country, warning that scientists may come under scrutiny. Kang says that there may well be other scientists under indictment who are scared to come forward and accuse the government of profiling.

"We are putting out the word to our networks," he said. "So they will know who to come to."