Fred Warmbier
Fred Warmbier, father of Otto Warmbier, speaks during a news conference in Cincinnati, June 15, 2017. Reuters/Bryan Woolston

The father of Otto Warmbier, a North Korean prisoner released Tuesday, blamed former President Barack Obama’s administration for not doing enough for his son’s faster release from the isolated country.

Last March, North Korea’s Supreme Court sentenced Warmbier to 15 years in prison with hard labor for stealing a political banner from a staff-only section of a Pyongyang hotel where he was staying. At the time the U.S. said it was working to secure Warmbier’s release.

Read: Why Is North Korea So Isolated?

He returned to the U.S. in state of coma after being detained in North Korea for over 17 months. He remained hospitalized after the flight carrying him landed in Ohio.

"The question is, 'Do I think the past administration could have done more?' I think the results speak for themselves," Fred Warmbier, the 22-year-old’s father said Thursday.

"We met everyone in the last administration from [then-Secretary of State] John Kerry to... our senators, our congressmen... Those were our efforts," Fred said.

North Korea said Warmbier fell into a coma after contracting botulism and taking a sleeping pill last March. However, Fred rejected the country’s explanation for his son’s condition.

"Even if you believe [the North Korean] explanation of botulism and a sleeping pill causing the coma, and we don't," Fred said. "There is no excuse for any civilized nation to have kept his condition secret and denied him top-notch medical care for so long."

Fred also said they followed the Obama administration to keep a low profile. The Warmbier family kept quiet "on the false premise that (North Korea) would treat Otto fairly and let him go."

Warmbier’s father noted that the State Department under Trump administration “was negotiating pretty tough with them."

"[Trump] told me a little bit about [Secretary of State] Rex Tillerson and [Special Representative for North Korea Policy] Joe Yun. You know, they teamed up, and they made things happen. You know, [the president] was very candid," Fred said. "To be honest with you, I had avoided conversations with him. Because to what end? … But I did take the call and it was gracious and it was nice and it felt good and I thank him for that."

Read: American Detained In North Korea Gets Help From Trump Administration

Fred also said ex-NBA star Dennis Rodman’s ongoing trip to the reclusive country did not aide in his son’s release. It was widely speculated that Rodman would take up the issue of U.S. citizens detained in North Korea. However, Rodman reportedly said the issue was “not my purpose right now.”

Meanwhile, doctors treating Warmbier at the University of Cincinnati Medical Center said he suffered extensive loss of brain tissue. He opens his eyes but does not show signs of understanding language or responding, Dr. Daniel Kanter, professor of neurology and director of the Neurocritical Care Program said.

"This pattern of brain injury is usually seen as result of cardiopulmonary arrest where blood supply to (the) brain is inadequate for a period of time, resulting in the death of brain tissue," Kanter said.