Washington (CNN) -- A Secret Service scandal involving agents who hired prostitutes in Colombia did not harm presidential security, according to an investigation conducted by the acting inspector general for the Department of Homeland Security.
"Although we found that these agents engaged in misconduct, our investigation developed no evidence to suggest that the actions of USSS (U.S. Secret Service) personnel in Cartagena compromised the safety and security of the president or any sensitive information during this trip," Charles Edwards wrote to House and Senate members concerned about the matter.
The findings support previous statements by the Secret Service that the actions of some agents who were in Colombia in advance of President Barack Obama's arrival for an April trip did not endanger the president.
Edwards said he does not plan to make the report public -- in accordance with his office's policy. But he provided some of the results.
Six women received money. As was previously known, an agent refused to pay one of the women who summoned a police officer. Another agent ended up paying the woman. Four women asked for money but did not receive any, while three others sought no payment.
Prostitution is legal in Colombia. But the news that some Secret Service agents were drinking heavily and taking prostitutes back to their hotel rooms raised security concerns and tarnished the reputation of the agency charged with protecting the president.
Edwards' letter also raised the possibility that two others involved in presidential trip preparations may have "had contact with foreign nationals."
"Although allegations related to the non-USSS (U.S. Secret Service) personnel were outside the scope of the investigation, one of these employees is a Department of Defense employee affiliated with the White House Communication Agency and the other, whose employment status was not verified, may have been affiliated with the White House advance operation," Edwards wrote to House and Senate members interested in the matter.
Edwards said a hotel registry led investigators to suspect the two might have come into contact with foreign nationals.
He wrote to members of Congress that the IG's mandate was just to look into the actions of the Secret Service so there was no further investigation.
Republican Sen. Susan Collins of Maine issued a statement saying she was "troubled that the IG's findings reveal White House personnel may have been involved." She said the White House press secretary said on April 23 that a review by its counsel's office concluded there were "no credible allegations of misconduct by anyone on the White House advance team or the White House staff."
"This raises concerns about the credibility of the White House investigation," said Collins, the ranking Republican on the Homeland Security and Governmental Affairs committee.
The White House denied staffers were involved in the incidents involving prostitutes.
"As we've said for months, the White House review concluded that no members of the White House advance team, either staff or volunteers, engaged in inappropriate conduct during the President's trip to Colombia,' said spokesman Eric Schultz.
A senior administration official said inaccurate hotel records implicated a volunteer working for White House advance. The White House review determined the volunteer "did not engage in any inappropriate behavior," the official said.
According to an August report by U.S. Southern Command, a total of 12 service members brought prostitutes to hotel rooms prior to the Obama trip.
Seven U.S. Army soldiers and two Marines were notified they would receive what the military calls "non-judicial punishment" for misconduct. A member of the Air Force got a letter of reprimand. The miltary said at the time it was continuing the investigation into the role of two members of the Navy in the scandal.
Thirteen Secret Service Agents were implicated in the prostitution scandal, including one who self-reported. Nine agents left their jobs or are in the process of being terminated. Four agents were cleared and returned to duty.
CNN's Lesa Jansen, Adam Levine and Mike Mount contributed to this report