Now, the only messages from Gadahn are vehemently anti-American statements that encourage violence.
"We love nothing better than the heat of battle, the echo of explosions and slitting the throats of infidels," Gadahn said. "If it's hard to imagine that any compassionate person could see pictures, just pictures of what the crusaders did to those children, and not want to go on a shooting spree at the Marines housing facilities at Camp Pendleton."
Stern said the problem is that Gadahn actually sounds somewhat reasonable. He is speaking about horrible acts that may or may not have been committed by American troops in Iraq, such as the alleged murder of 24 people in Haditha and the alleged premeditated rape of Iraqi woman and the killings of her and her family.
"This is our worst nightmare in a way, because incidents like that play right into the hands of people like this, who will use it as an opportunity to draw new recruits to the jihadi cause," Stern said.
ABC News' Kate Snow contributed to this report.