It's hard to believe, it's never happened before. That's what some lawmakers are telling the head of the Secret Service, at a Senate hearing on the prostitution scandal.

FOX News Radio's Jared Halpern reports from Washington:

Senate Homeland Security Committee Chair Joe Liberman says the Secret Service must find out if there's a culture of misconduct in the agency, admitting it's hard to believe 12 Secret Service agents, last month in Colombia:

(Liberman) "Suddenly and spontaneously did something they or other agents had never done before."

Secret Service Director Mark Sullivan describes the prostitution scandal as an isolated incident.

(Sullivan) "Senator, I'm hoping I can convince you it isn't a cultural issue."

Sullivan also says the prostitutes in Colombia posed no security threat.

In Washington, Jared Halpern, FOX News Radio.

Editor's Note: Director Sullivan did tell the committee there was an incident in 2008 where a Secret Service agent was arrested for trying to proposition a prostitute. It was a sting operation and the woman the agent thought was a prostitute, was actually part of local law enforcement.