The process of testing for CTE, according to brain researchers and experts who spoke with ESPN, involves preserving, dissecting, staining and examining tissue samples from different regions of the brain under a microscope. In the note, he repeatedly said he was sorry and asked that his brain be studied for CTE, according to police. But whether the gunman is diagnosed with CTE or not, experts cautioned against drawing direct connections between the shooting and the disease. "Multiple factors" come into play, Dr. Julia Kofler, a neuropathologist at the University of Pittsburgh, told ESPN, noting that "we don't really know how they relate to each other." "I think the connection between CTE and these acts of violence, it's impossible to really infer a causal relationship," Kofler told ESPN.