The deputy police chief in Fresno, California, was arrested on Thursday on charges of participating in multiple conspiracies to distribute heroin, oxycodone and marijuana, the FBI said.
Keith Foster, 51, was arrested along with three other residents of Fresno, about 170 miles south of Sacramento, an FBI statement said.
Two other Fresno residents also face drug charges but have not yet been arrested.
"It is important that we do everything we can to maintain and enhance the trust that our citizens have in us," Fresno Police Chief Jerry Dyer told a news conference after Foster's arrest. "When things of this nature happen, it does serve to erode that trust."
The arrests followed a year-long investigation by the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives that authorities said disclosed that Foster and others were involved in conspiracies to distribute oxycodone, marijuana and heroin.
Foster remains in custody and is to make an initial appearance on Friday, U.S. Attorney's Office spokeswoman Lauren Horwood said.
In December 2014, after filling a prescription for 100 oxycodone pills, Foster called a relative and said he had "100 of those things," an ATF agent said in a criminal complaint filed on Wednesday.
The agent said he believed Foster then drove to the relative's house with the intent of delivering the pills.
(Reporting by Eric M. Johnson in Seattle; Editing by Peter Cooney)