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(NBC) -- Polygraph tests appear to have cleared at least one Secret Service employee, but now there's word more military membersmay have been involved.

A 12th member of the military has now been relieved of his duties while investigators get to the bottom of who hired prostitutes while preparing for President Obama's trip to Colombia.

In Colombia, Defense Secretary Leon Panetta said accused service members have been stripped of their security clearances. "If these investigators find that there have been violations, uh, violations of the code of military justice, violations of the standards I just talked about, those individuals will be held accountable."

This latest member under investigation was assigned to the White House communications agency providing secure communication for The President.

White House attorneys did their own investigation last weekend, to see if any White House Staffers were involved. "That review was conducted and it produced no indication of misconduct," said White House Press Secretary Jay Carney.

The top Republican on the Senate Judiciary Committee wants details. In a letter to the White House, Senator Chuck Grassley is asking who was involved, how long did it take, was the Pentagon involved, and were hotel records reviewed.

And he wants answers by this Thursday.

A source close to Secret Service investigation says drugs tests on their personnel were negative.