PULLMAN, Wash. -

The Whitman County Prosecutor's Office decided Friday morning it will not pursue any charges in the case of injured Washington State University instructor Dr. David Warner. 

The prosecutor's office says there is not enough evidence to prove beyond a reasonable doubt that Warner was criminally assaulted. They say there is enough evidence to support that Warner suffered a serious injury, but not enough to support a crime occurred. 

Warner, 41, suffered a serious head injury during a confrontation involving five others outside the university owned Adams Mall on College Hill on March 30.

Four people were arrested, but prosecutors say a lack of clear video surveillance, differing witness statements and legal requirements for assault have led to their decision not to pursue charges. 

The prosecutor's office says, in this case, it was possible a friend Warner was with was pushed and fell into Warner, knocking him to the ground and causing him to hit his head.