Three North Koreans who crossed into South Korea in the East Sea on Saturday were repatriated to the North, as a daylong investigation uncovered no evidence of espionage activities, the Ministry of Unification said Monday.

A wooden boat and the three crew members were transferred to North Korean authorities in the afternoon after the ministry announced that they had departed for the inter-Korean sea border.

The government notified the North of the repatriation decision through the inter-Korean liaison office in Kaesong on Monday morning. The North did not respond to the South’s notification.

The fishing boat was taken to a South Korean port in Yangyang, Gangwon Province, for investigation by the South Korean Navy on Sunday, after violating the Northern Limit Line -- the de facto maritime border between South and North Korea -- late Saturday.

“What’s most important from a humanitarian viewpoint is the free will of the North Koreans. Based on that free will, we decided to repatriate them,” Unification Ministry spokesperson Lee Sang-min told a regular briefing.

During the investigation, the crew members told South Korean military authorities that they had accidentally taken the wrong sea route and had no intention of staying in the South.

In a briefing to reporters, the Joint Chiefs of Staff said it found no evidence to raise suspicion of espionage or other illegal activities based on the crew members’ testimony and their request for repatriation as well as the result of an inspection of the ship.

The 10-meter-long boat was filled with fishing gear and squid, and the engine was running normally when it was spotted. GPS was not installed on the vessel.

One of the North Korean crew members was wearing a military uniform, leading South Korean authorities to tow the boat due to the possibility that it could be a military vessel. The JCS said he was not a soldier.

In June, another North Korean wooden boat crossed the border in the East Sea undetected and docked at the South’s eastern port of Samcheok, Gangwon Province.

Among four men on board, two were sent back to the North while the rest defected to the South according to their wishes. The investigation of the four men took four days.

By Park Han-na (hnpark@heraldcorp.com)