A sign used as the backdrop for press briefings at the U.S. State Department, shown in a file photo from 2006. (Charles Dharapak/Associated Press)

In a city dense with black Chevrolet Suburbans and other official vehicles equipped for security details, a set of 15 attracted extra attention.

The 15 were stolen by what federal prosecutors say was a theft ring run out of the U.S. State Department’s protective equipment and armored vehicle division from 2011 until March.

James Ratcliffe, a longtime licensed auto seller from Northern Virginia, pleaded guilty in D.C. federal court Thursday to working for five years with an unnamed State Department insider to steal 15 unarmored official vehicles, including the ubiquitous Suburban model favored by the U.S. Secret Service and a low-mileage 2004 Hummer H2.

The vehicles were lost in the bureaucratic shuffle of the Diplomatic Security Service’s division, which in 2015 reported having more than 4,700 armored vehicles in use worldwide to protect missions and personnel, with another 783 awaiting shipment, repairs or assignment.

James Ratcliffe, 67, leaving federal court in the District on Thursday. ( Spencer S. Hsu/The Washington Post)

All but two of the stolen vehicles — “essentially unused” 2013 Suburbans, a black one and a white one, together valued at $96,400 — were sold by Ratcliffe for a profit, along with truckloads of tires and wheels, prosecutors said in charging papers. Ratcliffe, of Fairfax Station, pleaded guilty to felony conspiracy to defraud the government, punishable by a statutory maximum of five years in prison, although a plea agreement said federal guidelines would call for a sentence of 18 to 24 months.

The scheme allegedly brought Ratcliffe $408,520. The vehicles were sold from a Springfield shop that did maintenance work for the department and where Ratcliffe was a manager and previous owner, prosecutors said.

The vehicles were kept at the home where Ratcliffe, 67, and another unnamed conspirator who now owns the business live, court files state. They used the black Suburban with a dealer plate as their personal vehicle, prosecutors said.

“Are you pleading guilty today because you are, in fact, guilty?” U.S. District Judge Amit P. Mehta asked in court.

Ratcliffe answered, “Yes, sir.”

Mehta set sentencing for May 3 and released Ratcliffe on condition that travel beyond Virginia, the District or Maryland be cleared through probation officials.

Ratcliffe, whose plea deal requires him to return all proceeds, and his Bethesda attorney, Allen Orenberg, declined to comment afterward.

The repair shop’s owner did not return a telephone message left Wednesday with an employee.

Ratcliffe managed the Springfield company and was sole proprietor of a second business for about 32 years, authorities said.

Prosecutors charged that Rat­cliffe obtained the vehicles from the department employee, titled them under his business’s name, told buyers they were bought through such legitimate means as auctions, then paid kickbacks of cash or vehicles to the employee.

“The goal of the conspiracy was for the defendant, Person B, and others to enrich themselves by engaging in a conspiracy and a scheme to defraud in which they obtained property of the United States,” Assistant U.S. Attorney John Marston wrote, referring to the unnamed State Department employee responsible for buying, maintaining and keeping records of vehicles.