AP) — Senators investigating the Secret Service prostitution scandal said Wednesday that dozens of reported episodes of misconduct by agents point to a culture of carousing in the agency and urged Director Mark Sullivan to get past his insistence that the romp in Cartagena was a one-time mistake.

The disconnect between the senators and Sullivan reappeared again and again throughout the two-hour hearing, even as the Secret Service chief for the first time apologised for the incident that tarnished the elite presidential protection force. By the end, Sullivan’s job appeared secure even as new details emerged that left little doubt, senators said, that a pattern of sexual misbehaviour had taken root in the agency.

“He kept saying over and over again that he basically does think this was an isolated incident and I don’t think he has any basis for that conclusion,” said Sen. Susan Collins of Maine, the senior Republican on the Homeland Security panel that heard Sullivan’s first public accounting of the episode.

“For the good of the Secret Service,” added Sen. Joe Lieberman of Connecticut, the panel chairman, “he’s got to assume that what happened in Cartagena was not an isolated incident or else it will happen again.” Still, Sullivan insisted repeatedly that in his 29-year Secret Service career he had never heard anyone say that misconduct was condoned, implicitly or otherwise.

“I just do not think that this is something that is systemic within this organisation,” Sullivan said.

The misconduct became public after a dispute over payment between a Secret Service agent and a prostitute at a Cartagena hotel on April 12. The Secret Service was in the Colombian coastal resort for a Latin American summit before Obama’s arrival. Twelve employees were implicated, eight of them ousted, three cleared of serious misconduct and one is being stripped of his security clearance. Sullivan said two who initially resigned now are fighting for their jobs back.

“These individuals did some really dumb things,” Sullivan told the Senate panel. “I’m hoping I can convince you that it isn’t a cultural issue.”

He didn’t make much progress on that front, as senators offered fresh evidence of what they considered reckless behavior. Lieberman said 64 allegations or complaints of sexual misconduct were made against Secret Service employees in the last five years.

Three of those, Lieberman said, were complaints of inappropriate relationships with a foreign national and one of “nonconsensual intercourse,” on which he didn’t have enough information to elaborate. Sullivan said that complaint was investigated by outside law enforcement officers, who decided not to prosecute.

Thirty other cases involved alcohol, Lieberman said, almost all relating to driving under the influence.

Sullivan also told the committee an agent was fired in a 2008 Washington prostitution episode, after trying to hire an uncover police officer.

Charles Edwards, the inspector general at the Homeland Security Department conducting his own probe, and Sullivan discussed an episode from the 2002 Olympics when at least three agents were caught in a rowdy, drunken party in the agents’ hotel rooms with college-age women under 21, the legal drinking age.

They were accused of plying the women with alcohol, and two were accused of but not charged with sexual misconduct. One agent was charged with disorderly conduct. The agents involved left the Secret Service, Edwards and Sullivan said.

Against that backdrop, Colombia was probably not an aberration, lawmakers said.

“It’s just hard to believe that this is just a one-time occurrence,” said Sen. Ron Johnson, R-Wis.

But Sullivan stuck to that reasoning, pointing out that the dozen agents and supervisors implicated in the Colombia incident were a tiny fraction of the agency’s 7,000 employees.

“I can understand how the question could be asked,” Sullivan said, calling his employees “among the most dedicated, hardest-working, self-sacrificing employees within the federal government.”

He also told senators that Obama’s security was never at risk. The officers implicated in the prostitution scandal could not have inadvertently disclosed sensitive security details because their confidential briefing about Obama’s trip had not taken place.

“At the time the misconduct occurred, 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.

Collins dug in. She pointed out that several small groups of Secret Service employees separately visited clubs, bars and brothels and engaged in sexual and other conduct that could have exposed them to blackmail or coercion by foreign intelligence service, drug cartels or others.

She noted that two participants were Secret Service supervisors – one with 21 years of service and the other with 22 years – and both were married. Their involvement “surely sends a message to the rank and file that this kind of activity is tolerated on the road,” Collins said. Nor, she said, did they try to hide their activities. The agents signed themselves and their guests into the hotel registry.

Both she and Lieberman seized on Sullivan’s account of a government-wide survey taken that found only about 60 percent of Secret Service agents said they would report misconduct by their colleagues.

Lieberman told the hearing it is impossible to establish a historical pattern of Secret Service conduct from what is known so far.

But he said: “It is hard for many people, including me, to believe that on one night in April 2012 in Cartagena, Colombia, 11 Secret Service agents – there to protect the president – suddenly and spontaneously did something they or other agents had never done before.”

Prostitution is legal in Colombia, but Sullivan quickly issued new guidelines that made it clear that agents on assignment overseas are subject to U.S. laws.