WASHINGTON — In the hours after a Secret Service employee got into a dispute with a prostitute at a hotel in Colombia two weeks ago, high-ranking officials with the agency pored over hotel records.


The officials determined that a dozen agents and officers had had women in their rooms the previous nights, and they ordered the employees to return to the United States for questioning.


But one employee was particularly adamant that no one else had been in his room the previous night and that he had done nothing wrong.


“He was much more animated than anyone else,” said a government official who has been briefed on the investigation.


Despite the employee’s denials, agency officials did not believe him. The hotel kept records of which guests had had women in their rooms and required the women to leave copies of their identification cards at the front desk before going to a room.


As the employee was preparing to leave the country with the others who had had women in their rooms, the agency officials determined that he had been wrongly accused.


According to a senior American official, the agency has uncovered evidence from the hotel that on the night before, a member of the United States military took a woman back to the hotel and gave the Secret Service employee’s room number at the front desk when a copy of the woman’s identification was made. The member of the military is among the 12 service members under investigation for misconduct with women in Colombia before President Obama arrived. It is unclear whether the member of the military purposely gave the Secret Service employee’s room number or picked it at random.


The agency told the employee that he would remain in the country and be part of the team protecting President Obama.


Meanwhile, the Secret Service has begun to change its policies after the scandal. The agency plans to bar employees from drinking alcohol beginning 10 hours before their shift, the senior American official said. The previous cutoff was six hours.


Another detail about the prostitution case emerged on Thursday. According to a Congressional official, the employees involved included nine Secret Service agents and three uniformed officers. None were part of the president’s personal detail.