The announcement of a comprehensive review comes after independent watchdog agency had been sending mixed signals about what its role would be in the probe.
When Homeland Security Secretary Janet Napolitano testified on Capitol Hill last week, she told Grassley there is a standing agreement -- "a memorandum of understanding" -- between the Secret Service and the Inspector General that governs how internal investigations are conducted. "In these types of cases, where there is alleged misconduct, [the Inspector General] actually supervises the investigation but they use the investigatory resources of the Secret Service. That's how we are managing this one."
That is not, however, how the Inspector General's office described the arrangement in response to questions from ABC News last Wednesday, in an exchange that occurred after Napolitano gave her answer to the Senate.
Spokeswoman Rachael Norris told ABC News that the Inspector General is "closely monitoring" the Secret Service's investigation and will review it when it has been completed.
"We're monitoring their internal investigation at this time," Norris said. "We are not conducting an additional investigation at this time."
The Inspector General's subordinate apparently dated to 2003, when the Secret Service was moved from the Department of Treasury into the newly created Homeland Security department. Both the Secret Service and the Coast Guard, which was moved from the Transportation Department to DHS the same year, retained their internal investigative powers.
On Monday, however, the agency said the only reason it did not launch its own, independent probe was because the Secret Service already had investigators on the ground in Colombia.
"In our oversight capacity, and in recognition that there were already USSS Office of Professional Responsibility investigators on the ground in Colombia, we determined that the USSS was best positioned to immediately initiate the investigation with the full understanding that they would keep OIG informed as the investigation progressed," Edwards said. "We have maintained close contact with the USSS, coordinating with them as their internal investigation continued."