Sgt. Stephen Redfearn said Tuesday ambulances didn't arrive on the scene of the shooting July 20, 2012, quickly enough.
"After what seemed liked awhile, they were not getting through," he said. "So I decided we should start transporting victims in police cars."
Of the 60 victims taken to area hospitals -- many in the back of police cars -- all but two were saved, The Denver Post reported.
"That's a very courageous thing," Dr. Frank Lansville, medical director of emergency services at Medical Center of Aurora, told the Post in July 2012.
Redfearn's testimony was part of a debate over whether statements the suspected gunman, James Holmes, made on the scene can be used against him at trial because he wasn't first advised to his rights, the newspaper said.
Holmes faces multiple first-degree murder charges in the massacre that left a dozen people dead and 70 injured at a theater where a Batman movie was being shown. Holmes has pleaded not guilty by reason of insanity.
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