Officials said they've questioned 10 women and plan to question the other two women soon, The Washington Post reported Wednesday.
The Secret Service says 135 of 175 agents and officers deployed to Colombia for President Obama's trip to last month's Summit of the Americas stayed at the Hotel Caribe, where the scandal occurred.
The 10 women said they were paid for their encounters.
A Secret Service report given Thursday to the congressional committee investigating the scandal said nine of the 12 Secret Service employees allegedly involved have successfully completed polygraph exams. Three employees, whoever, have not cooperated with requests to take exams, CNN reported.
House Homeland Security Committee Chairman Peter King, R-N.Y., told CNN the three agents were among the first to lose their jobs in the scandal. One agent said in the polygraph test that he did not realize the woman was a prostitute and threw her out of the room when she said she wanted to get paid. King said the agent has not been fired.
House Oversight Committee Chairman Darrell Issa, R-Calif., and Rep. Elijah Cummings, D-Md., have said security personnel involved in the scandal showed an "alarming lack" of "character" and "judgment."
Twelve members of the military have also been implicated in the scandal.