A Korean-American who served prison time for attempting to broker the sale of deadly nerve gas bombs to Iran was indicted Wednesday on new charges of trying to help South Korea obtain advanced Russian rocket hardware and technology.

Investigators also found thousands of e-mails allegedly sent by Juwhan Yun, a 68-year-old naturalized U.S. citizen from Short Hills, N.J., involving other deals for sophisticated radar and air defense systems, short-wave infrared cameras, laser-guided bomb components and missile launch devices.

Yun is quoted in one e-mail as boasting that he has been "the largest one-stop supplier" of sensitive military and similar equipment for South Korea for the past 30 years.

Yun was arrested April 15 at the Fort Lauderdale airport after meeting with a former arms trafficker working as an informant for U.S. Immigration and Customs Enforcement and Defense Department investigators. The cooperating arms trafficker, who is not named in court documents, had previously worked with Yun on deals involving Russian SU-27 fighter planes and surface-to-air missiles.

Yun, who is being held without bail, faces up to 60 years in prison and $6 million in fines if convicted of all six charges, which involve attempting to broker or export prohibited defense or missile-related items and failing to register with the U.S. government as a broker. Yun's court-appointed attorney did not immediately return a telephone call Wednesday seeking comment, nor did officials the South Korean embassy in Washington.

The Justice Department and U.S. attorney's office in Miami also declined immediate comment.

In 1989, Yun was charged with attempting to supply Iran with 500 quarter-ton bombs of deadly sarin nerve gas. He was eventually convicted of conspiracy and sentenced to 30 months. He was released in March 1991. None of the gas was ever acquired by Yun or shipped to Iran.

In the new rocket case, based largely on intercepted e-mails and phone calls, Yun allegedly was trying to help South Korea acquire a rocket propulsion system — a joint Russian-U.S. system called the RD-180 — through Russian channels. The system was to be used for the Korea Satellite Launch Vehicle 2, according to court documents.

In one meeting in Fort Lauderdale, Yun allegedly told the informant that "he had excellent connections in the government of South Korea" and hoped that the informant's ties to Moscow would enable the deal to go through. Court documents indicate that South Korea had launched a rocket in 2005 using Russian technology, but the Russians had refused to make a similar deal for the second rocket launch.

Yun said in one e-mail that the Koreans were considering trying to get rocket technology from France, Germany or Great Britain. If the Russian deal could be worked out, he added, Yun was "certain that he and the (informant) could do very good business."