The U.S. has worked through the Swiss Embassy since 1955 to communicate with the North Korean government.  According to the Swiss embassy, we were notified that Warmbier's health was deteriorating, but not until March 2017.  A number of attempts were made in 2016 to gain his release, including a trip to North Korea by former governor Richardson.  It appears that in mid-2016 (plus or minus a month or two) Warmbier experienced a medical event causing brain damage.  The North Koreans refused further efforts by the U.S. to release him.  A few months ago the Swedish embassy was notified that his condition took a turn for the worse.