SEATTLE -- On Wednesday, the defense's main expert - a psychologist who analyzed Aaron Ybarra after the Seattle Pacific University shooting - took the the stand..

Neuropsychologist Dr. Craig Beaver visited Ybarra multiple times in jail after his arrest.

Due to Ybarra's mental disease, his delusions, his schizoaffective disorder, Dr. Beaver believes Aaron Ybarra is unable to understand how wrong his actions were when he shot three students, killing one of them - especially when it came to what Ybarra's "bizarre delusions," where someone believes an external force is seizing control of them.

"He had repeated talked with me that he had a hole in his brain and that Satan or Lucifer was taking control of him," said Dr. Beaver. " For example, he talks about Eric Harris, one of the shooters of Columbine, and his talk about how their minds merged."

Dr. Beaver also talked about how concrete and literal Ybarra is, that he answered questions very literally, depending on how the question is asked.

It sounds like the defense is trying to explain how he told police one story about what drove him to do it, and told a different one on the stand.

Ybarra is accused of fatally shooting Paul Lee, 19, and wounding two others. Ybarra has pleaded not guilty by reason of insanity to first-degree murder and other charges in the case. His trial began Oct. 10 and is expected to last two months.

KING 5's Elisa Hahn has been following developments in the trial. You can follow her updates on Twitter at @elisahahnk5 (App users can also click here to view updates on Storify).

Related stories:

Ybarra's testimony contradicts confession

SPU shooting suspect takes the stand

'Hero' in SPU shooting suspect takes the stand

Previous coverage:

SPU Shooting Trial - Week 1 - Live blog by Elisa Hahn

SPU Shooting Trial - Week 2 - Live blog by Elisa Hahn

SPU Shooting Trial - Week 3 - Live blog by Elisa Hahn