Update: Additional comments from medical team on significance of lack of botulism found in tests, included in text.

Doctors attending to the care of Otto Warmbier told media at a press conference on Thursday that they are unable to ascertain with certainty what caused the severe neurological injury he suffered in North Korea.

Doctors Daniel Kanter, Jordan Bonomo and Brandon Foreman of the University of Cincinnati Health Center however said that tests showed “extensive loss of brain tissue in all regions of the brain”. 

They also said that no signs of botulism were found, saying in a statement issued to