SEOUL, South Korea (AP) — South Korea deported two North Koreans on Thursday after finding they had killed 16 fellow fishermen on a boat and fled to South Korea across the sea border over the weekend.

The two North Koreans, both men in their 20s, were found aboard a boat south of the eastern sea border last Saturday, according to Seoul’s Unification Ministry. It said a South Korean investigation later found the two had killed 16 colleagues aboard a fishing boat and escaped to South Korea.

Details of the alleged onboard killings weren’t immediately known.

South Korea has a policy of accepting North Koreans who wants to resettle in the South to avoid political oppressions and economic poverty at home. But a Seoul Unification Ministry spokesman, Lee Sang-min, said South Korea has decided to send the two fishermen back to North Korea because they allegedly committed “grave” crimes and couldn’t be protected by the South Korean government.

Lee said South Korea expelled the men to North Korea via an inter-Korean border village on Thursday. He said Seoul on Tuesday had informed Pyongyang of their planned deportations and that North Korea on Wednesday responded it would accept them.

Lee said Seoul has determined the two’s acceptance to the South Korean society would threaten its own public safety.