Sorrento Police Chief Fern Barnett heard a knock on a door at her home about 9 p.m. Wednesday while she was reading, went to answer and saw the lights of a vehicle pulling out of her driveway off La. 22.

She looked out and saw a Bushmaster M4 on a bench under her carport.

The semi-automatic rifle has been missing from the Police Department since July, if not longer, according to department invoices and police asset inventories.

“I have no idea who left it,” Barnett said Thursday.

The Police Department bought the rifle in 2007 from an Alabama gun dealer when the department was trying to form a SWAT team.

Barnett, who agreed to leave her post by late March as part of a payment settlement with the town, has been trying to get a handle on the equipment in the largely defunct, one-person department as the town moves to dissolve it and surplus its property.

In November, voters overwhelmingly decided to abolish the chief’s post and the department after former Chief Earl Theriot Jr. left under a cloud and was convicted of lying to an FBI agent about having inappropriate sexual contact with a drunk woman. Barnett won the job in October by default after two other candidates dropped out of the Nov. 4 election to replace Theriot.

Barnett said she got indications that something was amiss with the department weapons inventory in mid-December as she went through town asset lists and an audit showing that the department once had three Bushmaster rifles but more recently had only two.

At the suggestion of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, Barnett said, she requested another outside federal inventory list and invoices from the company that sold the three Bushmasters to the town in 2007.

“By the middle of January, I was sure I was looking for a gun,” she said.

Barnett said she reported the missing rifle to the ATF and to the Ascension Parish Sheriff’s Office, has been calling former police officers and Theriot about the gun, and has been putting out word that anyone could drop it off at the department or her house.

Barnett said former Assistant Chief Ricky Smith, who compiled an inventory list in July that documented only two Bushmasters and worked the next month with auditors who documented the same thing, told her that he doesn’t remember the rifle ever having been in police inventories since he was hired in 2010.

Smith’s list dates the two other Bushmasters as being in inventory since June 5, 2010. It’s not clear what happened to the third weapon between that June date and Wednesday night.

Even before the mystery drop-off, Barnett said, she had sent the Sheriff’s Office a letter Monday asking that deputies store all the department’s guns until they can be safely disposed of.

But with the revelations of the missing rifle Monday, Sheriff Jeff Wiley said he had already been planning to do the same thing and sent deputies to the department Thursday to retrieve the weapons.

“Before the sun goes down today, all those weapons will be in my armory, locked down and safe and sound and fully accountable,” Wiley said Thursday.

Barnett said deputies arrived at her office about 11 a.m. Thursday and took the department’s weapons.

The Sheriff’s Office has been providing police protection to Sorrento since November 2013 — initially on a part-time basis and later on a full-time one — after the department lost its liability insurance. In December, the town agreed to a long-term contract with the Sheriff’s Office.

Barnett said she has doubts whether an investigation into who had the Bushmaster could go anywhere. She said sheriff’s deputies have not taken fingerprints of the rifle. She doubted doing so would do any good and questioned what could be proved if any fingerprints of former police officers were found on the rifle.

Sheriff Wiley said information is limited and the one person who might know anything, Barnett, can’t say who dropped off the rifle.

“I’m telling you I don’t know what else we can do,” he said.

Special Agent Kevin Moran, spokesman for the ATF New Orleans Division, said the agency had not opened an investigation into the missing weapon as of Wednesday afternoon but has been serving in an advisory role to the Police Department.

Follow David J. Mitchell on Twitter, @NewsieDave.