JUDY WOODRUFF: Now to the release of Otto Warmbier from captivity in North Korea.

The American college student was arrested almost 18 months ago during a trip to the reclusive nation, and he was sentenced to 15 years in prison.

This morning came word suddenly that the United States had secured his release, but under apparently desperate circumstances. Warmbier is comatose, and has been for a year. An American delegation in Pyongyang petitioned for his immediate release yesterday.

Our chief foreign affairs correspondent, Margaret Warner, reports.

REX TILLERSON, U.S. Secretary of State: At the president's direction, the Department of State has secured the release of Otto Warmbier from North Korea.

MARGARET WARNER: The announcement came from Secretary of State Rex Tillerson at a Senate budget hearing. The 22-year-old University of Virginia student was finally free, after being jailed by the North's repressive regime for 17 months.

Anna Fifield has been reporting the story for The Washington Post.

She spoke via Skype from Tokyo.

ANNA FIFIELD, The Washington Post: What I have been told is that, last Monday, June the 5th, the North Koreans actually approached Americans who they talk to, and they said that Otto Warmbier was in a coma and had been in a coma for more than a year.

And that started the ball rolling to have him medically evacuated. The North Koreans said that he came down with a case of botulism soon after his sentencing, and that he was given a sleeping pill and fell into a coma, and he didn't wake up from that.

MARGARET WARNER: Warmbier's parents confirmed their son is in a coma, and had been medically evacuated.

In a statement to the Associated Press, they also said: "We want the world to know how we and our son have been brutalized and terrorized by the pariah regime."

Warmbier was arrested after he allegedly took a propaganda poster from the wall of a Pyongyang hotel on New Year's Eve, 2015. He'd been in North Korea as part of a tour group. In March last year, he was sentenced to 15 years hard labor.

OTTO WARMBIER, Released North Korean Prison: I have made the worst mistake of my life.

MARGARET WARNER: In the past, Pyongyang has used detained American citizens to try to exert leverage over the U.S.

But Anna Fifield says, this time, the North had appeared unwilling to bargain. It didn't respond to U.S. offers to send a high-level envoy to discuss Warmbier and three other Americans held by the North. One was arrested just last month.

Pyongyang's attitude changed in May. It agreed to let Swedish diplomats visit the prisoners, and with news of Warmbier's dire condition, Pyongyang urgently requested a meeting with a top U.S. official at the U.N. last week.

At that point, Fifield said, President Trump got involved.

ANNA FIFIELD: Once Otto Warmbier's condition was known, I'm told that the president did become involved, that he was informed, that he personally gave the order to do everything that they could to get Otto Warmbier out.

MARGARET WARNER: The release comes at a time of heightened tensions between Washington and the regime of Kim Jong-un. Pyongyang has ramped up its nuclear and missile programs. In response, the U.S. has taken a tough tack, and recently began deploying the advanced anti-missile defense known as THAAD to South Korea.

But Fifield says another motivation may have driven the North Koreans.

ANNA FIFIELD: I think the North Koreans have probably realized that they did need to get rid of Otto Warmbier at some stage, that he wasn't recovering, and they needed to hand him back.

MARGARET WARNER: The release also coincides with former NBA player Dennis Rodman's latest visit to Pyongyang. Fifield says she was told Rodman's visit had nothing to with the freeing of Warmbier.

Warmbier was flown first to an American military medical facility in Japan, then flown on to Cincinnati, near his family's home.

For the PBS NewsHour, I'm Margaret Warner.