WASHINGTON (CNN) -- Three Iraqis testified Tuesday in a federal grand jury investigation of a deadly Baghdad shooting involving security contractors from Blackwater Worldwide.
The three men refused to comment on what they told the panel or their reaction to testifying in the closed-door proceedings, which began in November.
Prosecutors also declined to speak to reporters about what the Iraqis said.
According to Iraqi officials, Blackwater guards shot and killed 17 people, including women and children, and wounded 27 at Baghdad's Nusoor Square on September 16.
Though a number of Blackwater guards have testified in the proceedings, Tuesday marked the first time that Iraqis have appeared before the panel.
Blackwater officials have said the incident began when armed insurgents attacked its guards. But the first U.S. soldiers who arrived on the scene told investigators they found no evidence that the guards were fired upon, sources familiar with the investigation have previously told CNN. See details about security contractors in Iraq »
One of the men who testified, Mohammed Hafez Abdul Razzaq, was an eyewitness to the incident. His 9-year-old son was killed in the shooting. He previously was interviewed by FBI agents in Iraq, as were other wounded civilians and eyewitnesses.
The grand jury has been meeting since November as prosecutors try to determine if the guards broke U.S. laws.
Blackwater is one of three contractors providing security services for the State Department in Iraq. The other two are Triple Canopy and DynCorp.
Under a provision instituted in the early days of the U.S.-led occupation of Iraq, security contractors have immunity from Iraqi law.
The incident placed the operations of Blackwater and other security firms under scrutiny in Iraq, where an estimated 25,000 private contractors protect diplomats, reconstruction workers and government officials.
Blackwater's five-year State Department contract, which began in 2006, must be renewed every year. In April, the contract was renewed amid controversy over the pending legal action.