A neighbor might have helped stop a Colorado man from killing three people as he roamed around with a military-style rifle, but the state’s open carry law apparently prevented police from following up on her concerned report.

Naomi Bettis called 911 Saturday after spotting her neighbor, who she recognized but did not know by name, walking outside his home with an AR-15 rifle, reported the Denver Post.

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“He did have a distraught look on his face,” Bettis said. “It looked like he had a rough couple days or so.”

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However, the 911 dispatcher declined to send police and reminded Bettis that Colorado allows gun owners to legally and publicly carry their firearms out in the open.

Police eventually did respond — but not until 33-year-old Noah Harpham had already shot two women and a man with the rifle that had concerned his neighbor at least several minutes earlier.

Authorities identified the victims Monday evening as 35-year-old Andrew Alan Myers, 42-year-old Jennifer Michelle Vasquez, and 34-year-old Christina Rose Baccus-Gallela.

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Police responded shortly before 9 a.m. Saturday to a report of a possible shooting, and they found Myers dead and a fire burning, according to dispatch logs.

Witnesses said Harpham shot his victims one by one as they begged for their lives.

“It looked totally random,” said neighbor Matthew Abshire, who followed the gunman and called the police. “He walked calmly and collectedly. His demeanor was like he was having a stroll in the park.”

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Police fatally shot Harpham about seven minutes after they first arrived at the scene, but not before he killed his victims one by one — including a bicyclist who begged for his life.

It’s not clear at this point how much time passed between Bettis’ call and the first shooting — which prompted a flood of 911 calls.

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But the case stands in contrast to at least three others in states that permit the open carry of firearms.

Dispatchers declined to respond to the report about Harpham, who was white, and reminded the caller, who is also white, that Colorado is an open carry state.

However, dispatchers in Ohio sent police to two calls last year involving John Crawford, a black man, and Tamir Rice, a black boy, who were each shot and killed on sight by law enforcement officers — although they were each carrying toy weapons in an open carry state.

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Another black man, Darrien Hunt, was fatally shot by police who responded to a report of him carrying a sword — which turned out to be a replica — along a commercial boulevard.

Ohio allows the open carry of firearms, and Utah became the second state to pass a law prohibiting cities from banning the carry of knives — which swords are generally considered to be by weapons advocates.

None of the officers involved in those fatal shootings were charged.

Watch an interview with Bettis posted online: