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A fully automatic M-16 rifle went missing from the Davis County Sheriff's Office, probably sometime before 2006, according to an investigation by that office.

The U.S. Department of Defense provided 20 M-16s to the sheriff's office in 1998. Except for a few training exercises, the rifles sat in storage until 2006, when they were issued to deputies.

But there's no record of the missing rifle having been issued, according to a report from the sheriff's own detectives.

"This investigation has been inconclusive as to where the missing weapon is," a detective wrote in his report's conclusion. "The weapon is listed" in a nationwide law enforcement database "and if that is how it is located, then a criminal investigation will commence."

Davis County Sheriff Todd Richardson said last week it's only a matter of time before the rifle is found. And anyone who knowingly possesses the rifle will be prosecuted, even if that person is or was a peace officer.

"If it was procured by somebody who found it," Richardson said, "they are in possession of a stolen rifle and they're going to suffer consequences for it."

The Pentagon provided the rifles through its 1033 Program, which gives surplus weapons and other gear to law enforcement. Sixty-two Utah law enforcement agencies are eligible to receive equipment through the program. Items such as emergency blankets and sleeping mats become property of the police department, but the Defense Department maintains ownership of the weapons and can require they be returned at any time.

When a March 2013 audit revealed one M-16 in Davis County was missing, all of Utah was suspended from the 1033 Program, according documents the state provided to The Salt Lake Tribune. Utah was reinstated the next month, when Davis County adopted a corrective-action plan.

Richardson, who was elected in 2010, said his office has revamped its weapons policy. Rifles are now assigned to individuals rather than vehicles, and administrators conduct periodic inspections to ensure each individual has his or her weapons.

The sheriff said his office was in the process of adopting such a policy when the audit revealed the M-16 was missing.

Richardson assigned two detectives to look for the rifle. According to their reports, the M-16s arrived in 1998 but sat in storage until 2001 or 2002. Sometime in that two-year span, the rifles were assigned to the person responsible for the sheriff's firing range and armory.

The detectives interviewed deputies and others who worked in the armory or were in sheriff's administration between 2001 and 2006. There were conflicting accounts of whether the rifles were ever deployed for training, including a regimen in Idaho, according to the reports.

"We had a hard time trying to find training records that far back," Richardson said.

All former sheriff's employees denied having the rifle.

The detectives also searched for the rifle at the sheriff's headquarters and storage facilities in Farmington. Sergeants were ordered to search the vehicles of their subordinates. One former employee remembered an M-16 being loaned to Clearfield police. Clearfield police searched its armory for the rifle, according to the reports.

At a meeting of police chiefs from Davis County, the sheriff's chief deputy asked them whether anyone had the rifle. No one reported finding the M-16.

The detectives did find the triggers for the automatic firing function on the other M-16s. They were removed before the M-16s were issued to deputies in 2006. But there was no trigger for the missing M-16, suggesting the weapon went missing before 2006.

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