This link takes you to the 26:46 minute mark in this interview. This interview is with a former high-ranking North Korean government official who defected to South Korea in 2016.

He states he worked in the offices where is colleagues handled Warmbier. American doctors found no clear signs he was tortured.

He is 80% sure North Korea poisoned 22 yo Warmbier after making him publicly admit to being a spy.

He said the poison is undetectable and that N. Korean has developed and stockpiled enough chemical weapons to kill everyone on earth.

The whole video is pretty interesting and goes in to how the Kim regime operates.