Federal prosecutors are seeking to dismiss their case against the Temple University professor accused of selling sensitive U.S. defense technology to entities in China.

Prosecutors declined to elaborate on the decision, but Xiaoxing Xi's attorney said Friday that the U.S. Attorney's Office and the FBI had fundamentally misunderstood the complex science their case hinged on, and backed down when confronted with their mistakes.

"It is an extremely technical area," said Peter Zeidenberg, the lawyer. "That's the problem. It's very technical, and I think what happened is that certain assumptions were made that were incorrect."

After being charged in May with four counts of wire fraud, Xi remained a faculty member at Temple but stepped down as chairman of the physics department.

Prosecutors had said Xi, who is regarded as a leader in superconductor research, in 2002 worked at a U.S. company that invented a device, known as a pocket heater for magnesium diboride thin films, that revolutionized his field. A year later, he purchased the device to continue his testing, and signed an agreement to not reproduce, sell, transfer, or attempt to reverse-engineer the device.

In their indictment, prosecutors accused Xi of violating the agreement, citing 2010 emails he sent to Chinese contacts that they maintained included the schematics for a pocket heater.

But Zeidenberg said that in a meeting last month, he presented prosecutors with affidavits from experts, including the inventor of the pocket heater, who said prosecutors were mistaken: The device being depicted was not a pocket heater.

"It was our contention all along that these emails were innocent and did not reflect the transfer of any restricted information or information that was covered by a nondisclosure agreement," Zeidenberg said. "I think the government simply misunderstood what was being discussed in these communications."

Zeidenberg said Xi was not cooperating with prosecutors on any other investigations as a condition of the case's being dismissed.

In a motion to dismiss, filed late Friday, prosecutors said that since they filed the charges, "additional information came to the attention of the government" that warranted the case's being dropped.

A spokeswoman with the U.S. Attorney's Office declined to comment further. The office asked to dismiss the case without prejudice, meaning it could be revived.

A judge has yet to rule on the motion.

Xi's daughter, Joyce, reached at the family's Penn Valley home, said her father was not available.

"We're relieved that the indictment against my father has been dismissed," she said.

Zeidenberg said the ordeal had been "absolutely devastating" for Xi, who pleaded not guilty and posted $100,000 bail after his arrest.

"A dozen armed agents came into his home and took him away in handcuffs in front of his family. So it's been, you know, a traumatic experience, and he's extremely relieved that this is over," Zeidenberg said.

Thin-film research allows engineers to eliminate resistance in the conduction of electricity, and has applications ranging from building smaller circuits for smartphones to improving speed in computers. The research also has military applications.

Temple spokesman Ray Betzner said it was "too soon to say" whether Xi would be reinstated as chairman.

"We're very pleased that with this matter behind him, Professor Xi can once again turn his full attention to conducting his research," Betzner said.