Former U.S. president Jimmy Carter left North Korea on Friday after securing the release of Aijalon Mahli Gomes, an American man who was sentenced to eight years of hard labor and fined $700,000 for illegally entering the country in April. Carter arrived in North Korea Wednesday for the private humanitarian mission, but it is not known if he met with North Korean leader Kim Jong-il. South Korean officials say a train believed to be carrying Kim entered China around midnight on Wednesday, setting off speculation over what might have compelled him to leave the country while Carter was visiting. South Korean intelligence officials speculated that Kim may have been taking his youngest son and presumed successor, Kim Jong-un, to formally introduce him to Chinese leaders. Other possible motives include the North’s need for Chinese aid because of flooding and the possibility of a decline in Kim’s health, which might have forced aides to take him to China for treatment.