Iraqi authorities arrested a British contractor Sunday over the shooting deaths of two co-workers in Baghdad's protected Green Zone. The suspected gunman could be the first Westerner to face an Iraqi trial on murder charges since a security pact lifted the immunity that had been enjoyed by foreign contractors for most of the war. The gunman shot his colleagues -- one British and one Australian -- during a quarrel, then he wounded an Iraqi while trying to flee their compound inside the vast area that is sealed off from the rest of the capital, Iraqi officials said. "It started as a squabble," Iraqi military spokesman Maj. Gen. Qassim al-Moussawi told the Associated Press. "The suspect is facing a premeditated murder charge. The matter is now in the hands of Iraqi justice." He said the suspect was being held at an Iraqi police station in the Green Zone.