Four security officers at a government facility were arrested Tuesday after allegedly demanding payouts from other guards in exchange for passing marks on their mandatory weapons recertifications, authorities said.

A Prince George's County grand jury last week indicted four employees of North American Security on several counts including theft, extortion and conspiracy in connection with the scam, which ran over a three-year period starting in 2014, said John Erzen, a spokesman for the Prince George's County State's Attorney's Office. The company is contracted to provide security for the National Oceanic and Atmospheric Administration building in Silver Spring, Md.

The employees arrested were in charge of running weapons recertifications for the NOAA guards or were supervisors, Erzen said. After guards took their exams at Maryland Small Arms Range in Upper Marlboro, those running the program told participants that they had failed but could receive their firearm certifications if they paid anywhere from $150 to $500, Erzen said.

At least seven guards agreed to pay, Erzen said, noting that those who were told that they had failed were never shown any results. At this point, he said, investigators don't believe that anyone who paid actually did fail.

"Here you have someone trying to lawfully work and support their families, and then someone turns around and extorts them," Erzen said.

The four arrested were Craig Hymon, 41, of Gaithersburg; Diamond Mabry, 27, of Capitol Heights; Chidinma Ileka, 36, of Beltsville; and Vicson Johnson, 43, of Temple Hills. It was unclear Tuesday whether any of the defendants had obtained attorneys.

After the investigation came to light, guards at the facility were required to get recertified as a safety precaution, Erzen said.

The case began as an internal investigation within the Commerce Department, which oversees NOAA, said Clark Reid, a spokesman for the department's office of the inspector general.

"Our office of the inspector general brought this to the attention of the State's Attorney's Office and Maryland State Police and worked with them to execute the arrest warrants," Reid said.

Art Lopez, chief executive of North American Security, said that the allegations were troubling and that he was "at a loss for words." The company employs about 75 guards at the NOAA facility in Silver Spring, he said.

Lopez said he knew that authorities were conducting an investigation and the company had been cooperating, but he wasn't made aware of the specific allegations.

"We have a transition plan we're implementing to be able to ensure we provide the best service," Lopez said. "We're working on a change in command and training issues."

Lopez said the company will probably order an independent investigation from an outside firm in the future to "find out where the soft spots are."