The hearings started in Washington D.C. earlier this week. Members of Congress accused the ATF of allowing about 1,800 guns to be smuggled into Mexico for use by drug cartels.
The basic idea was to let the guns be used in crimes that ATF agents could then use to gather evidence to build bigger cases. One of those weapons surfaced in the murder of Border Patrol agent Brian Terry in Arizona.
The House Oversight and Government Reform Committee introduced ATF agents who testified they tried to stop the gun walking program.
In the hearings, representatives from the Department of Justice declined to address the questions because they could jeopardize ongoing investigations.
Arizona Republican Paul Gosar said the Justice Department has failed to respond to subpoenas.
"We need compliance with the subpoenas," Gosar said. "To find out who and who all understood what was going on and signed off on this."
The hearings will continue throughout the summer. The Office of Inspector General has also opened an investigation into the matter.