A lawyer for three activists removed from one of President Bush's town hall events said Thursday that the Secret Service has opened a criminal probe into whether the man who escorted them from the hall was impersonating an agent.

The man was dressed in a dark suit and wore an earpiece when he escorted the three from the March 21 event. The Secret Service (search) has said it has determined the man was not one of its agents, but a staff member with the host committee.

An agent from Washington, D.C., contacted attorney Dan Recht (search) and asked if his clients — Alex Young, Karen Bauer and Leslie Weise — could be interviewed this week, Recht said.

The lawyer said he declined the request unless the "mystery" man's name and organization were released.

Jonathan Cherry (search), a Washington, D.C.-based spokesman for the Secret Service, said he could not comment on the case.

The White House (search) has said the man was a volunteer who probably feared the three might have disrupted Bush's event. Bauer, Young and Weise acknowledge they wore T-shirts under their clothing that read, "Stop the Lies," but did not plan to reveal them.

The three belong to an activist organization called Denver Progressives. The day after being escorted out of the event, they say they were told by the Secret Service they were singled out because they belonged to the "No Blood for Oil" group. They do not belong to such a group, but a bumper sticker on their car said "No More Blood for Oil."

The man who escorted the three out did not identify himself, but he threatened Bauer and Weise with arrest if they "did anything" and told them they had to leave because it was a private event, the women said. The three had tickets to the event.

Members of Colorado's congressional delegation from both parties have raised concerns about the case.