Fresno Deputy Police Chief Keith Foster was among four who were arrested Thursday as part of a federal drug investigation.

The arrests, which were announced during a press conference at the Fresno FBI office, were a product of an ongoing, yearlong, joint investigation conducted by the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives.

Foster, 51, who oversaw the police department’s four patrol operations districts as the second-highest ranked officer in the department, was arrested for conspiracy to distribute oxycodone, heroin and marijuana.

Also arrested were Rafael Guzman, 41, for conspiring with Foster to distribute heroin; Randy Flowers, 48, for conspiring to distribute oxycodone; and Jennifer Donebedian, 35, for conspiracy to distribute marijuana.

Fresno Police Chief Jerry Dyer said Foster will be placed on administrative leave, during which time he will be stripped of his police powers. Dyer said he was notified of the investigation — which featured several surveillance techniques such as wire taps — after Foster was arrested.

“I’m at a loss for words,” Dyer said. “When something like this happens, it has an impact. Things of this nature serve to erode the trust members of this community have on this police department.”

Foster has served as deputy police chief since 2007, Dyer said.