WASHINGTON - Conflicting images of the Secret Service and new questions about the military's handling of the prostitution scandal in Colombia emerged Wednesday on Capitol Hill.

Senators challenged Homeland Security Secretary Janet Napolitano to reconcile the image of agents who protect the president's life with the dozen implicated officers and supervisors.

Meanwhile, the Defense Department acknowledged to other lawmakers that it knew that six military personnel had broken curfew rules prior to President Obama's arrival at a Latin American summit in Cartagena but let them remain on the job. In addition to the Secret Service officers and supervisors, another dozen military personnel also were implicated in the prostitution scandal. The chairman of the Senate Armed Services Committee, Carl Levin (D., Mich.), questioned the military's decision.

"That may have been the right decision, but it nonetheless raises an interesting question as to whether ... that was an appropriate decision to let them continue on the mission, given the seriousness of the mission," Levin told reporters.

The Defense Department on Wednesday briefed Levin and Sen. John McCain (R., Ariz.) about its investigation. McCain complained afterward that the Pentagon officials who met with them "provided appallingly little new information" and were "woefully unprepared to answer even the most basic questions about what happened in Cartagena."

Navy Capt. John Kirby, a Pentagon spokesman, said the Defense Department would keep Congress "as informed as possible as the investigation proceeds."

Testifying at an oversight hearing, Napolitano told the Senate Judiciary Committee that the incident involving as many as 20 women appeared to be an isolated case. She said the agency's Office of Professional Responsibility had never received previous complaints in the last 21/2 years. It was unclear why she specified that period.

Sen. Lindsey Graham (R., S.C.) pressed Napolitano about whether she believed this was the first incident involving prostitutes.

"If there hadn't been an argument between one of the agents and, I guess, a prostitute, for lack of a better word, about money, we'd probably have never known about this," he said.

If the misconduct is part of a pattern, Napolitano said, "that would be a surprise to me."

The Secret Service announced this week that all 12 implicated officers or supervisors had been dealt with: eight forced out, one stripped of his security clearance, and three cleared of wrongdoing, all within two weeks of the night in question.