Sen. Joe Lieberman tells CNN's "State of the Union" that he believes the agency has done a thorough job in investigating the incident. But the Connecticut independent also wants to know whether there were warning signs about agents' behavior.
He also wants to hear what steps are being taken to ensure something similar doesn't happen again.
Lieberman says the Secret Service director, Mark Sullivan, will be called to the hearing by the Senate Homeland Security and Governmental Affairs Committee.
