The deputy chief of the Fresno Police Department in California has been accused for working on the other side of the law and was arrested for distributing and possessing drugs.

Keith Foster, 51, the Fresno Police Department's second in command, was arrested on Thursday in a federal drug conspiracy investigation led by the FBI and ATF. The 51-year-old veteran cop is now facing charges for distributing and possessing oxycodone, marijuana, and heroin. Three other people connected to Foster were also arrested on federal drug charges, said authorities, reports The Associated Press.

Federal investigators announced that they collected surveillance evidence of Deputy Chief Foster, without revealing further details about the investigation. Investigators also used telephone wire taps during the yearlong investigation.

Foster, who climbed the ranks to become a deputy chief eight years ago, has since been placed on paid administrative leave.

"This is a very sad day for the Fresno Police Department, the citizens of Fresno, and the law enforcement profession," said Fresno Police Chief Jerry Dyer during a news conference Thursday afternoon, reports NBC News.

"The message I want to send to everyone, when we place this badge on our chest, it's a badge of honor. There's a lot of responsibility that goes along with it. It is important that we do everything we can to maintain and enhance the trust our citizens have in us," he added, assuring that his officers are not above the law, reports ABC 30.

The other suspects named in the case are Fresno residents Rafael Guzman, Jennifer Donebedian and Randy Flowers.

Foster, a 29-year-veteran of the Fresno Police Department, was in charge of overseeing patrol operations for the department's four police districts.

The Fresno Police Department released a statement saying that the Fresno police will also conduct an internal investigation into accusations of criminal and policy violations.