Sam Carter was charged with attempting to influence a public official, forgery and tampering with evidence after he shot the elk while on duty on a snowy New Year's Day 2013.
Prosecutors say Carter, fascinated with the elk, stalked it for days and sought to mount its head on a wall as a trophy. They said he shut off the GPS in his squad car when he shot the animal, and failed to radio dispatchers his location. Prosecutors said Carter later forged a tag to pass off the dead animal as road kill.
But his attorney, Marc Colin, said the elk had become dangerously domesticated and aggressive, frightening local dogs. The trial opened with debate over whether the elk's prior "bad conduct" could be used as evidence, and whether jurors familiar with Big Boy could be impartial.
"Sam Carter is not guilty of anything but trying to protect citizens of Boulder from a nuisance elk," Colin said, as some in the packed courtroom shook their heads.
Prosecutors flashed a photo of the elk looking peaceful in a yard, and later showed another picture of a uniformed Carter hovering over the animal's carcass, grabbing its antlers and smiling.
Prosecutors say Carter called another officer, Brent Curnow, to come cart away the body in his pickup truck, and together they butchered the animal for its meat. Curnow pleaded guilty last year to tampering with evidence and other charges and is expected to testify against Carter.
The officers swapped text messages about "hunting" for "wapiti," the Shawnee word for elk. The exchanges culminated with a stark message from Carter to Curnow well before Carter's shift began: "He's gonna die."
Nestled against the foothills and home to a Buddhist university, Boulder is known for its love of the outdoors. Its residents routinely rank among the country's most fit.
For many, the trial has reopened old wounds. Witnesses who testified on behalf of the elk said the sight of the hulking animal was a highlight on countless hikes and jogs.
"Maybe we're strange, but the philosophy up here is live and let live," pet supply store owner Mary Lee Withers told The Associated Press in an interview. "That elk never did anything."
Withers would encounter the elk on walks with her St. Bernard. Her neighbors sometimes found it sleeping in their yards. She is helping raise money for a memorial bench, which she said will be cut from sandstone and have porcelain inlays bearing the elk's likeness.
The case also inspired a Boulder man's tribute song, "Reason to Kill (Ballad of Big Boy)." Its visceral lyrics include: "Gunned down for nothing, But his sovereign space, Wrong time, wrong place."
"He was not a pet, but he was a fixture of Mapleton," Withers said. "He had been there for years."