Who are the three U.S. prisoners released by North Korea?

Donald Trump spent the early hours of Thursday morning loitering on the tarmac of Joint Base Andrews to greet three Korean-American prisoners, who hours earlier had been released by North Korean leader Kim Jong Un.

The president personally greeted Kim Dong Chul, Kim Hak Song and Tony Kim, who landed on U.S. soil just after 2 a.m. ET. The trio flew home with Mike Pompeo after the secretary of state traveled to Pyongyang to secure their release — part of the ongoing rapprochement that will culminate in a summit next month between Trump and Kim.

Trump boarded the plane with his wife Melania to greet the freed three, before emerging at the top of the steps to wave to the cameras.

“This is a special night for these three really great people,” Trump told reporters, before congratulating the men for “being in this country.”

Trump said he “very much appreciated” that Kim had released the prisoners as an act of goodwill ahead of their meeting.

READ: Kim says denuclearization “achievable” in second secret meeting with Xi

“I really think he wants to do something, and bring that country into the real world,” Trump said. “I really think a lot of progress has been made… some great things can happen.”

Singapore has emerged as the likely location for the summit, according to officials in Seoul and Washington.

While the three men appeared in good health, they were transported immediately to the military's Walter Reed Medical Center in Washington for a thorough health check.

Who are the three freed men and why were they imprisoned in North Korea?

Kim was arrested on May 7, 2017, but the details of why remain a mystery. The state-run KCNA news agency said he had been arrested for “hostile acts” toward the state.

An agricultural expert, Kim was in North Korea working at the Pyongyang University of Science and Technology, teaching rice-growing. In a statement at the time, the school, which is North Korea’s first privately-run university, said he was apprehended after concluding a trip to carry out “agricultural development work” at the school’s “experimental farm.”

Kim, an ethnic Korean, was born in Jilin in China, but educated in California. He is believed to have emigrated to the U.S. in the mid-1990s and he was also ordained an evangelical Christian pastor affiliated with the Oriental Mission Church in Los Angeles.

Also known by his Korean name Kim Sang Duk, Kim was detained at Pyongyang airport on April 22, 2017, as he was leaving the country.

Also a teacher at PUST, Kim was accused of attempting to overthrow the North Korean government. KCNA reported at the time that Kim “was intercepted for committing criminal acts of hostility aimed to overturn the (Democratic People's Republic of Korea) not only in the past but also during his last stay before interception.”

Kim taught accounting at PUST, but in an interview with the New York Times the university chancellor said Kim was involved in some extracurricular activities, such as volunteering at an orphanage.

Kim trained as an accountant in California and worked in the U.S. for 10 years before returning to Korea.

A naturalized American citizen, Kim was arrested in 2015 on accusations of espionage and other undisclosed crimes. The 62-year-old was born in South Korea but is a resident of Fairfax, Virginia.

When arrested he was running a trade and hotel services firm in the special administrative zone between China and North Korea.

His detention only came to light three months after his arrest when he was presented to a CNN television crew. He was sentenced to 10 years hard labor for his crimes in 2016, just weeks after Washington imposed steeper sanctions on Pyongyang over ongoing missile tests.

In a staged press conference, Kim reportedly admitted publicly to spying for “South Korean conservative elements” since 2013, as well as bribing North Korean residents for information about Pyongyang’s nuclear weapons program.

Cover image: Donald Trump applauds as US detainee Kim Dong-chul gestures upon his return with Kim Hak-song and Tony Kim after they were freed by North Korea, at Joint Base Andrews in Maryland on May 10, 2018. (SAUL LOEB/AFP/Getty Images)