SEOUL (Reuters) - The South Korean spy agency's assertion that North Korea purged its defence chief and executed him with anti-aircraft fire is one of its boldest claims ever, and, given the agency's chequered history, has come under growing scrutiny.
South Korea's National Intelligence Service (NIS) has a daunting major task - to look into arch-enemy North Korea, one of the world's most insular and hostile nations, and find out what's happening in its corridors of power.
The agency correctly revealed in 2013 that Jang Song Thaek, ruler Kim Jong Un's uncle and the second most powerful man in North Korea, had been purged. Among its misses, it failed to learn of the death in 2011 of leader Kim Jong Il, the current ruler's father.
The scepticism over the latest assertion stems from the NIS' evident certainty that Hyon Yong Chol was ousted as defence chief, although it will not publicly disclose its evidence, while it has said it is less certain he has been executed.
The NIS says it has intelligence of the execution but notes there has been no confirming statement from Pyongyang, and archival footage that includes Hyon continues to appear on state TV. However, the same reasoning appears to undermine its confidence of Hyon's purge, as people removed from office in Pyongyang also tend to drop out of state media, although not necessarily immediately.
Hyon, typically active in public events alongside Kim, has been absent from any mention in North Korea's official media since April 29, around the time the NIS says he was executed.
"I think they were too early to come out (with the news). NIS is playing a big, risky gamble," said Cheong Seong-chang, a North Korea watcher at the Sejong Institute and a critic of the NIS's handling of its information on Hyon.
"If it turns out NIS was wrong, it would be a huge embarrassment and put a dent in their ability to collect information," he said.
The secretive NIS took the rare step this week of sharing 11 pages of documents with a group of journalists to back up its assertions, although it does not reveal its sources.
"In regard to the execution, they had reliable evidence," said Kim Kwang-jin, an opposition lawmaker briefed by the NIS on Wednesday.
"Although they were not video or photos, the NIS was confident. But as public sentiment has worsened, it appears they are being less bold," he said.
North Korea, heavily sanctioned by the United Nations for its missile and nuclear tests and technically still at war with the South, is perhaps the world's most reclusive state, forcing South Korea's spies to rely on human sources.
Occasional midnight radio broadcasts of recorded strings of numbers originating in South Korea and heard across the border, a tactic that dates to the Cold War, are a signal that Seoul has agents in the North.
North Korea recently arrested two South Koreans it said confessed to spying on behalf of the NIS from the Chinese border city of Dandong. The NIS denied that they were spies.
The credibility of South Korea's intelligence organs has at times been undermined by political scandals and a history of unsavoury acts. A former head of the NIS was sentenced in February to three years in jail for meddling in the 2012 presidential election and trying to help Park Geun-hye win the vote. [ID:nL4N0VJ3F6]
The agency launched a special panel in 2004 to address its predecessors' histories of mysterious deaths and disappearances under past governments, and to open old files. It investigated the abduction of dissident and future president Kim Dae-jung by its predecessor, the KCIA, or Korean CIA.
But several observers say the agency would have little to gain from going public with such a bold assertion as Hyon's execution if it wasn't reasonably confident.
"Given my experience, when the agency calls the parliament first and gives a briefing on a North Korea issue, the intelligence must have been crossed-checked multiple times with every possible method, such as human intelligence and technical intelligence," said Jun Ok-hyun, who retired from the NIS in 2009 and was consul general in Hong Kong from 2010 to 2012.
"But due to the nature of North Korea as a closed state and little accessibility to public information, South Korean intelligence officials are inevitably left to deal with controversies after public disclosure of intelligence," he said.
Additional reporting by James Pearson in Seoul; Editing by Tony Munroe and Raju Gopalakrishnan