WASHINGTON - On any weeknight five months ago, Xiaoxing Xi could have been working in a laboratory at Temple University, the mild-mannered professor mentoring the dozen graduate students who flocked to the campus last year to work alongside the world-renowned researcher.

Wednesday, however, a soft-spoken Xi sat before an audience in Washington to speak about the last four months - a time he said has been defined by "tremendous" amounts of suffering as he fell under suspicion as an economic spy in a case that has since been withdrawn.

Now, the 57-year-old Penn Valley researcher has become the latest unlikely poster child for critics who say federal prosecutors have been too quick to charge Chinese American scientists in economic espionage cases.

In the last 10 months, federal prosecutors have withdrawn high-profile cases against four Chinese American scientists around the nation who had been accused of spying for China or Chinese companies.

Their treatment is illustrative of what several prominent Chinese Americans are calling a new wave of racial hysteria reminiscent of the Cold War red scares of the 1950s.

"The government is pulling the trigger too fast on these cases," said Brian Sun, a lawyer who has worked on high-profile economic espionage cases involving Chinese Americans, during Wednesday's panel discussion on the issue. "Not everybody is a victim of racial profiling and a rush to judgment, but I'll tell you this much: There are far too many cases of Chinese Americans who are."

Appearing Wednesday alongside his lawyer, Peter Zeidenberg, and Sherry Chen, an Ohio woman of Chinese descent who also faced economic espionage-related charges that were later dropped, Xi chronicled the effects of the charges upon his family and his life - including his stepping down as chairman of Temple's physics department. He said after the event Wednesday that he intends to resume his post, but first must have that conversation with the university's dean.

"I changed in a moment from someone who was a free man to someone who was under indictment," Xi said. "Suddenly I'm receiving the advice, 'Don't talk to people.' "

Federal prosecutors in May alleged that Xi had shared sensitive U.S. technology in emails to Chinese contacts in "an effort to help Chinese entities become world leaders in the field of superconductivity."

But last week, the Justice Department dropped the case, noting only that "additional information came to the attention of the government." Xi's lawyer, meanwhile, said that prosecutors had fundamentally misunderstood the technology Xi was accused of stealing.

Corporate espionage

The Obama administration has accused Chinese spy agencies of encouraging their nation's businesses to steal trade secrets from American corporations.

In the last year alone, the number of cases involving economic espionage by foreign entities has jumped 53 percent, the FBI said in July. The effect, the bureau said, citing an independent study, has been "hundreds of billions" of dollars in losses of American intellectual property.

The Justice Department has responded with cases filed against Chinese workers in the United States, alleging thefts of everything from Boeing aircraft schematics to details of how to make the pigment used to whiten the stuffing in Oreo cookies.

The latter theft led to what federal prosecutors touted as a significant victory last year: the convictions of two former DuPont scientists and an outside engineer for selling the secrets of the coveted cookie chemical - which is also in production of various plastics - to a competitor controlled by the Chinese government.

But cases such as Xi's and other recent prosecutorial missteps may be doing more harm than good to the Justice Department's cause, activists and legal experts say.

"There's no question that the Chinese government and Chinese companies are seeking to steal trade secrets and engage in economic espionage against the U.S. government and U.S. companies," said Peter J. Toren, a former federal prosecutor who specialized in computer crimes and industrial espionage. "But if you're going to seek these cases, you better be damn sure that you've got strong evidence."

Cases withdrawn

Since last year, prosecutors have also withdrawn charges against Chen, an Ohio-based hydrologist for the National Weather Service, who was accused of illegally accessing a government database and lying about meeting with a high-ranking Chinese official. At Wednesday's event, Zeidenberg called the case against Chen "aggressive and over-the-top" - one that would never have emerged, he said, if she were not a Chinese American.

As in Xi's case, federal authorities offered little in the way of explanation for their move regarding Chen, citing only "prosecutorial discretion."

That decision came only five months after the Justice Department dropped a similar case against Guoqing Cao and Shuyu "Dan" Li, former senior biologists at the pharmaceutical giant Eli Lilly & Co.

Such cases have drawn attention from groups ranging from the Congressional Asian American Pacific Caucus to the Committee of 100, a group of influential Chinese Americans founded by architect I.M. Pei and cellist Yo-Yo Ma. The latter group sponsored Wednesday's panel discussion.

Both groups have called on U.S. Attorney General Loretta Lynch to reexamine the investigations that led to the scientists' arrests.

"When it is multiple cases - all linked by the same fact that the Americans happened to be of Chinese ethnicity - then we have a constitutional and civil rights problem," Rep. Ted W. Lieu (D., Calif.) said in a statement issued this week. "Otherwise innocent actions do not become nefarious simply because the Americans taking those actions happened to have ethnic surnames."

Helen Zia - author of a book on the case against Wen Ho Lee, the former Los Alamos nuclear scientist accused of spying in 1999 before the case against him collapsed - called the government's handling of Xi's prosecution and other recent cases "unsettling."

"What has happened in Professor Xi's case is another example of what is going on, on a much larger scale," she said. "Every ethnic Chinese American scientist - no matter how long they have been in the U.S., no matter what good they have been doing to support and protect and build our country - they are all potential suspects in the current political climate."

Declining comment

The allegations against Xi largely centered on a device known as a pocket heater, a specialized piece of technology that revolutionized Xi's field, with uses ranging from small circuits for smartphones to military applications.

He was charged with four counts of wire fraud and was arrested in his Penn Valley home in front of his wife and two daughters.

For reasons as yet unexplained, prosecutors withdrew the charges "without prejudice" - meaning they have not ruled out charging Xi anew.

The U.S. Attorney's Office in Philadelphia declined again Wednesday to comment on the case.

Xi's lawyer said that the device depicted in Xi's emails was not the pocket heater investigators believed it to be.

Xi said Wednesday that his case and similar ones have broader consequences than just on those who are directly involved. When prosecutors incorrectly identify scientific collaboration as "something evil," Xi said, "our academic freedom is under threat."

"I see an urgent need for the academic community and other agencies to reach out to law enforcement and educate them, because it's obviously clear that they don't know what collaboration is like," Xi said. "They look at everything like criminal activity."