Chung was employed by the Rockwell International defence firm from 1973 until its defence and space unit was acquired by Boeing in 1996.
 
Formerly from China and now a naturalised US citizen, he held secret security clearance when he worked at Rockwell and Boeing on the space shuttle programme, officials told Reuters news agency.
 
Boeing said on Monday that they had been co-operating with the government on the case.

Secret documents

In the second case, Tai Shen Kuo, a New Orleans businessman, is accused of working with an unnamed Chinese official to obtain secret documents from Gregg William Bergersen, a US defence department employee.

A third person, Y
u Xin Kang, a Chinese citizen now resident in the US, is accused of acting as a "conduit of information" between Kuo and the Chinese official, the AFP news agency reported.
 
According to court documents, the alleged spying took place over a two-year period from January 2006 to February 2008.
 
Kuo is accused by the justice department of having held a series of meetings with Bergersen in northern Virginia, Charleston, South Carolina, and Las Vegas.
 
On some occasions, Bergersen, a weapons systems policy analyst, "received undetermined cash payments from Kuo in exchange for information and documents he provided," a justice department statement said.
 
"Today's prosecution demonstrates that foreign spying remains a serious threat in the post-Cold War world," Kenneth L Wainstein, assistant attorney general for national security, said in a statement.