SEOUL, South Korea — Secretary of State Mike Pompeo left North Korea on Wednesday with three U.S. detainees who were released ahead of an upcoming meeting between President Donald Trump and North Korean leader Kim Jong Un.

Here is a look at the three Americans, who were held by North Korea for alleged subversion, espionage and other unspecified hostile acts.

Tony Kim, 59, an academic who also goes by Kim Sang-duk, was detained April 22, 2017, at the Pyongyang airport on suspicion of committing “criminal acts of hostility aimed to overturn” North Korea, according to the North’s Korean Central News Agency.

Kim taught accounting at the Pyongyang University of Science and Technology and previously taught at the University of Science and Technology in China’s Yanji province, which borders North Korea. Kim graduated from the University of California at Riverside with a master’s degree in business administration in 1990.

He made at least seven trips to North Korea to teach. His wife accompanied him on the visit when he was arrested, though she was allowed to leave the country.

Kim Hak Song worked in agricultural development at an experimental farm run by the Pyongyang University of Science and Technology. He was detained May 6, 2017, and accused of engaging in unspecified “hostile acts” against North Korea, the news agency reported. It didn’t say whether his case was related to Tony Kim’s.

The university also said his detention wasn’t related to his work at the school.

Kim Dong Chul, 64, is a South-Korean-born U.S. citizen and the longest-serving detainee among the three Americans.

Kim was arrested Oct. 2, 2015, at a hotel in the capital city of Pyongyang on suspicion of spying. He was sentenced to 10 years in prison with hard labor in April 2016. He had lived in Fairfax, Va., before moving to China’s Yanji province near the North Korean border. From there, he commuted daily to a special economic zone in the North Korean city of Rason, where he established a company dealing in international trade and hotel services.

Before his sentencing, Kim apologized for slandering North Korea’s leadership, collecting and passing confidential information to South Korea, and joining a smear campaign against the North’s human rights situation. Other foreigners have been presented at news conferences in North Korea and admitted crimes against the North, but many said after they were released that their confessions were given involuntarily and under duress.

“I’m asking the U.S. or South Korean government to rescue me,” he told CNN in 2016.