ATLANTIC BEACH, Fla. – Atlantic Beach Police Chief Mike Classey resigned Tuesday morning in the wake of being the subject of an active criminal investigation, according to the Atlantic Beach Police Department.

Classey was placed on administrative leave Friday after the city was informed of the investigation being conducted by the Florida Department of Law Enforcement. His resignation is effective immediately.

Sources told News4Jax on Tuesday that the FDLE investigation is related to the illegal purchase of steroids from Mexico.

Classey's neighbors said FDLE investigators served a search warrant at Classey's East Arlington home Friday, when they removed an unusually large collection of guns.

Classey's colleagues said Classey is apologetic about the embarrassment this brings to the department, which he was appointed to lead in 2008.

"Just never would have guessed," Atlantic Beach Mayor Carolyn Woods said. "You don't expect someone in charge of the law in your city to be investigated for being on the other side of it. So yes, very surprised."

Woods said Classey did the right thing in stepping down immediately.

"Obviously, his resignation this morning was the right thing to do," Woods said. "Obviously, it does leave us in a bit of a lurch, but we are moving forward as quickly as possible to start the process of finding a new chief to the city."

The city has started contacting police agencies across the country, searching for a replacement. In the meantime, an interim chief has been appointed.

"The people of Atlantic Beach can be confident the department will function as it has," city manager Nelson Vanliere said. "Vic Gallilo will take over and be in charge."

Classey was home Tuesday but didn't answer the door. Vanliere said he spoke with Classey Tuesday morning and he was disappointed in himself.

"He's remorseful, he's apologetic to be putting us through this," Vanliere said. "We hope he goes on and gets his issues straightened out."

Vanliere said Classey's resignation is not tied to the Police Department or his job.

Residents were stunned by the news of the resignation on Tuesday.

"Are you kidding me? Atlantic Beach? That's wild, it really is, because you never hear much about Atlantic Beach where it comes to problems with law enforcement," beaches resident Ralph Cromley said. "You hear about Jacksonville Beach but never Atlantic and Neptune beach."

Locals also said they were disappointed the chief was under criminal investigation.

"That is uncalled for. You're a head chief. I don't know what to think about it," Chuck Ballard said. "You think he would be doing his duty and I just, me personally I would try to do best I can."

Police said Classey's resignation and the investigation will not have any bearing on any criminal cases pending in Atlantic Beach.

The Police Department said it will not issue any additional details, referring all questions to FDLE.