Senior prosecutor Kim Soo-Nam told a news conference Thursday that Lee and his colleagues specifically brought up possible targets to attack, including a telecommunications facility in Seoul, during the May meeting, which drew 130 people. He said the plotters also discussed using websites to find ways to manufacture firearms and bombs. According to transcripts of conversations at the meeting publicized by South Korean media, some participants talked about ways to make more powerful BB guns and searching the Internet to find ways to build homemade bombs.
Kim said Lee believed that high tensions between the two Koreas this past spring would lead to war.
"It's an incident that an underground revolutionary organization ... systemically and collectively plotted to overthrow a free democracy and posed a grave threat to" South Korea's national security, Kim said.
He said Lee was indicted on two others charges inciting a rebellion and praising North Korea in violation of South Korea's anti-Pyongyang security law. Three of Lee's colleagues were also indicted, he said.
Defense lawyers for Lee said in a statement that prosecutors still lack decisive evidence to back up their indictment.
Earlier this year, North Korea sharply raised tensions by threatening nuclear war in anger over toughened U.N. sanctions over its third nuclear test in February. Animosities have gradually eased since then.