A federal jury convicted a Chinese-born engineer Thursday of conspiring to export U.S. defense technology to China, including data on an electronic propulsion system that could make submarines virtually undetectable.

Chi Mak also was found guilty of being an unregistered foreign agent. Prosecutors had dropped a charge of actually exporting defense articles.

Mak, 66, acknowledged during the trial that he copied classified documents from his employer, a defense contractor, and kept copies in his office. He maintained he didn't realize at the time that making the copies was illegal.

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When the verdict was read, Mak at first showed no emotion but then appeared to hold back tears as a defense attorney rubbed his back. Both defense attorneys seemed emotional.

Assistant U.S. Attorney Greg Staples said Mak faces up to 35 years in prison when he is sentenced Sept. 10.

"We were confident from the start and we're very happy with the verdict," Staples said.

Staples said the government may use the verdict against Mak to try to negotiate plea bargains with other members of his family who are awaiting trial.

"Anything could happen. We haven't thought that far," the prosecutor said.

Authorities accused Mak, a naturalized U.S. citizen, of taking thousands of pages of documents from his employer, Power Paragon of Anaheim, and giving them to his brother, who passed them along to Chinese authorities over a number of years.

Mak was arrested in 2005 in Los Angeles after FBI agents stopped his brother and sister-in-law as they boarded a flight to Hong Kong.

Investigators said they found three encrypted CDs in their luggage that contained documents on a submarine propulsion system, a solid-state power switch for ships and a Power Point presentation on the future of power electronics.

His wife, brother and other relatives also have been indicted and are awaiting trial later this month.

The six-week trial featured testimony from a parade of FBI agents, U.S. Navy officials, encryption and espionage experts and the engineer himself.

Key to the trial was the government's allegation that Mak confessed to the conspiracy — and even named his so-called "handler" and specific restricted documents — during an untaped jailhouse interview two days after his arrest.

Mak testified he never confessed during that interview, but admitted on cross-examination that he lied repeatedly in an earlier taped interview about the number of times he had visited China and when he told authorities he didn't have friends or relatives there. He said he felt intimidated during the interrogation.

"This is why I lied," he said. "They were pushing me that night."

Mak's attorneys focused on the propulsion system documents found in his brother's luggage at Los Angeles International Airport.

Mak said he believed he was doing nothing wrong by giving the documents to his brother to take out of the country because they were papers that had been presented previously at international conferences.

The government, however, alleged the documents were export-controlled and couldn't fall into foreigners' hands.