An official says six South Koreans recently repatriated home from North Korea had sneaked into the North in search of better lives but ended up detained for up to 45 months for illegal entry.
North Korea sent back the six men and a woman's corpse Friday in an unusual action seen as an attempt to improve strained ties between the rival countries.
A South Korean security official said Monday the men told investigators they entered North Korea from China between 2009 and 2012 after suffering business failures and family troubles or engaging in pro-North Korea activities in South Korea.
One of the men told investigators that he killed his wife while in North Korea.
The official requested anonymity because an investigation was under way.