Story highlights The FBI says Darrell Mathis sold marijuana to federal agents during a 4-month probe

Mathis turned up in his patrol car, in uniform, for some sales

The investigation began with a "social visit," court papers state

Mathis could not be reached for comment; he could face up to life in prison if found guilty

An undercover sting operation nabbed an Atlanta-area sheriff's deputy who was selling marijuana out of his patrol car and in uniform, federal authorities say.

Newton County Deputy Darrell Mathis told an informant that he could sell pot without fear because "he drives safely and flashes police credentials to get out of tickets if stopped," according to court papers. Mathis, a five-year veteran deputy, was freed on bond after his arrest last week, the FBI said.

"This defendant used his position as a police officer to openly violate the very laws that he was sworn to uphold," U.S. Attorney Sally Quillian Yates said in a written statement. "Selling marijuana out of his police car while wearing a badge and uniform is outrageous. This case is a reminder that no one is above the law."

Mathis has been charged with possession of marijuana with intent to distribute and with carrying a firearm during a drug offense -- a charge that could bring a possible life sentence if convicted. He did not immediately return messages seeking comment Sunday.

Newton County is about 30 miles east of Atlanta. Sheriff Ezell Brown said Mathis has been placed on administrative leave, and his office is cooperating with the investigation.

"This is an embarrassment to the Newton County Sheriff's Office, as well as law enforcement in general," Brown said in a joint statement with Yates.

According to the charges against him, Mathis attracted the attention of the FBI in April after what officials called a "social visit" by a person who went on to become a confidential informant. The informant visited Mathis at his apartment and saw large bags of what was "believed to be marijuana" on the living room table.

The complaint states that Mathis told the informant that he wasn't concerned about getting caught, because of his safe driving and police credentials.

Apparently unnerved by the exchange, the informant went to the authorities and offered to help with an investigation. The FBI then set up a half dozen meetings among Mathis, the informant and eventually two undercover agents, court papers recount.

Mathis and the informant discussed a drug sale during their next meeting, the charges state. Mathis sold the informant an ounce of marijuana later that day, showing up for the deal in his cruiser, in uniform and carrying his service pistol.

After that, an undercover agent got involved -- and the amounts of marijuana increased.

In June, as the agent bought a pound of pot, Mathis boasted, "I do my little 10 to 15 a week" -- a phrase the agent "understood to mean selling 10 to 15 pounds a week," the arrest affidavit states.

Then in early August, according to the complaint, Mathis met with another undercover agent, a supposed cocaine dealer. The two agents and Mathis sat down at a restaurant to discuss buying and transporting marijuana and cocaine, according to the complaint.

While the three spoke, Mathis allegedly pulled out his badge and told the undercover agent, "Don't worry, I'm on your side." By the end of the meeting, the complaint alleges, Mathis had agreed to run marijuana and cocaine from Alabama to North Carolina at the behest of the undercover agent.

Federal agents found a pound of pot on Mathis when he was arrested last week, the FBI said.