Dozens of police officers and emergency responders converged at Rose Medical Center following reports of an "active shooter" on Friday.
They found neither a suspect nor any victims – and today police offered an explanation of how the situation might have evolved.
The incident began when staff at the hospital saw a man walking across a street near the facility. He appeared to be carrying a rifle, according to multiple witness statements.
Police still aren't sure whether or not he was carrying a weapon – but surveillance footage seems to show that the man had picked up the object from an alley near 9th Avenue and Colorado shortly before the calls went out.
Dispatchers received one call and several text messages about the man, beginning around 4:17 p.m.
The sighting of a potentially armed person prompted the hospital to declare a lockdown. Shortly afterward, a group of nurses on the second floor thought they heard shots on the fifth floor, and called that into police.
In fact, they may have simply heard doors slamming during the lockdown procedure, according to Division Commander Pat Phenan.
Police searched for hours for a shooter inside the building, ultimately coming up empty. They found no evidence of gunfire, and no evidence that the person ever approached the hospital.
They are still looking for a person in his mid 30s, weighing about 130 pounds and wearing a flannel shirt, a white cowboy hat, maroon shirt and white tennis shoes.
Police had little choice but to respond in force, Phenan said, given that they were receiving plausible reports of a shooter. "That's the safe way to do things," he said.