What happened to Otto Warmbier in North Korea?

This documentary tells the story of US student Otto Warmbier. He was sentenced to 15 years in a North Korean labor camp in 2016. He got released the next year, but died of brain damage shortly after his return to the US.
Was he a victim of torture? At the time, US president Donald Trump tweeted that Otto “had been tortured beyond belief”.
Trump blamed both the Obama administration and North Korean leader for the death of the student. But he later changed his tune at the relations between the US and North Korea became warmer.
What really happened to the young student? This documentary tries to find out. The documentary shows interviews with a number of people with knowledge to the case. And some of them reveal unheard information before.