With Mark Schapiro's investigative report, "The Middleman," FRONTLINE/World begins an ongoing series about the frightening world of nuclear smuggling. In a rare moment of agreement during last year's presidential debates, George Bush and John Kerry both declared nuclear proliferation as the single most serious threat the United States faces. Their bipartisan concern followed revelations that the father of Pakistan's nuclear bomb – A.Q. Khan – had sold nuclear secrets to Libya, Iran and North Korea. U.S. investigators have not been allowed to question Khan, who is still considered a national hero in Pakistan. 

In a joint investigation with the Center for Investigative Reporting and Mother Jones magazine, FRONTLINE/World correspondent Schapiro probes the strange case of a South African businessman, Asher Karni, who attempted to export 200 nuclear bomb triggers from the U.S. to Pakistan via Cape Town. The importer was Humayun Khan, an Islamabad businessman with close ties to Pakistan's military.

This is our first installment in Schapiro's probe of the Karni case – a report that appears in the May/June issue of Mother Jones. We also include photos and video clips, which will be part of a web-exclusive video investigation based on Schapiro's and producer Cassandra Herrman's recent trip to South Africa.