WASHINGTON — Secret Service Director Mark Sullivan apologized Wednesday before a Senate panel for the prostitution scandal that’s embarrassed his agency, but he said he didn’t believe that it had arisen from an agency culture of misbehavior.

But skeptical lawmakers questioned whether it was truly a one-time event, though they offered no evidence to suggest otherwise.

The chair of the Senate Committee on Homeland Security and Governmental Affairs, Sen. Joseph Lieberman, said he did find a record of 64 instances of sexual misconduct in the past five years. But Lieberman, a Connecticut independent, said he’d found no pattern in the events, which included a number of reports of sexually explicit emails or material on a government computer. Three involved an "inappropriate relationship" with a foreign national, he said.

Sen. Susan Collins, R-Maine, called the behavior of agents who took prostitutes back to their hotel rooms before a presidential visit to Colombia “morally repugnant” and said she doesn’t believe that it was an isolated incident. She noted that some of the participants were supervisors.

“That surely sends a message to the rank and file that this kind of activity is tolerated on the road,” she said. “The numbers involved, as well as the participation of two senior supervisors, leads me to believe that this was not just a one-time event. Rather, the circumstances unfortunately suggest an issue of culture.”

Sullivan said the agency "recognized the potential compromise related to the type of behavior engaged in by these employees" – taking prostitutes back to their hotels in Cartagena – but found "no adverse information" to indicate security breaches after checking with the intelligence community.

He said that none of the individuals involved in the misconduct "had received any specific protective information, sensitive security documents, firearms, radios or other security-related equipment in their hotel rooms."

Sullivan said there were about 200 Secret Service personnel in Cartagena when the misconduct occurred: Nine were found to have been involved in "serious misconduct" and three ultimately were cleared.

Sullivan said several times that he was “confident” that there wasn’t a Secret Service culture that accepted such behavior. He noted that the agency had investigated allegations of similar misconduct in El Salvador, but he said it had found no evidence to back them up.

Both senators said they continued to have confidence in Sullivan, but were pleased to hear that the inspector general of the Department of Homeland Security is conducting a separate investigation.