BOULDER, Colo. (AP) — A pharmacist who survived a 2021 mass shooting at a Colorado supermarket said Thursday during the gunman’s trial that she heard him say, “This is fun” at least three times during the shooting. The chilling detail had not been revealed before.

Sarah Chen said she heard the comments while hiding with her coworkers and carefully listening for any sounds from the plexiglass barrier at the pharmacy counter that might alert them to the shooter’s presence after Ahmad Al Aliwi Alissa had opened fire in the college town of Boulder.

“I heard him screaming, ‘This is fun. This is fun,’” Chen said.

No one, including Alissa’s lawyers, disputes he was the shooter. Alissa has pleaded not guilty by reason of insanity in the shooting.

Alissa was diagnosed after the shooting with treatment-resistant schizophrenia. His attorneys say he had hallucinations that included hearing screaming voices, seeing people who weren’t there and believing he was being followed in the runup to the shooting. They argue he should be found not guilty because he was not able to tell the difference between right and wrong at the time of the shooting.

He is charged with 10 counts of first-degree murder, multiple counts of attempted murder and other offenses, including having six high-capacity ammunition magazine devices banned in Colorado after previous mass shootings.

Testimony began Sept. 5, and the trial is scheduled to finish by the end of the month.

Another pharmacy worker, Maggie Montoya, a professional runner, testified about what she saw and heard while hiding in a room next to the pharmacy. That included hearing Alissa say he was naked while he surrendered. She didn’t mention hearing Alissa say, “This is fun.”