Marine Staff Sgt. Frank Wuterich had never seen combat before a roadside bomb tore into the supply convoy he was shepherding through the Iraqi town of Haditha and killed one of his men.

In the instants that followed, the rookie squad leader had only the experience of classroom exercises to guide his reaction. Hesitation, he said, could have been fatal.

"We had practiced this scenario before, in classrooms, on whiteboards, in front of superiors, subordinates and peers," he said. "The threat had to be neutralized."

Wuterich is accused of murdering 17 Iraqi civilians in the aftermath of the bomb blast, including women and children who were killed in their homes as Marines went on a house-to-house sweep.

He said in an unsworn statement before a military court Thursday that he had done the best he could.

"Based on the information I had at the time, based on the situation, I made the best decisions I could have at that time," he said. "Engaging was the only choice."

Wuterich also said he will "always mourn the unfortunate deaths of the innocent Iraqis who were killed during our response to that attack."

He spoke on the final day of preliminary hearings to determine whether he will be court-martialed over the 2005 incident in the town of Haditha.

Under military law, prosecutors could not cross-examine Wuterich about the killings that sparked the biggest criminal case against U.S. troops in the war in Iraq.

In all, 24 civilians were killed by Wuterich's squad in the aftermath of a bomb blast on Nov. 19, 2005.

Wuterich, 27, of Meriden, Conn., is accused of unpremeditated murder in 17 of the killings.

At his preliminary hearing, Marine Corps officials were trying to determine if his actions were consistent with his training and with combat rules in place at the time.

He previously said he was following rules of engagement that were then in place, and that he attacked the houses because he thought gunfire was coming from them.

On Thursday, Wuterich said Haditha was "ominously quiet" as his men rolled out on a supply run the day of the attack. After the bomb exploded and rained shrapnel on a Humvee carrying Wuterich, the mission quickly shifted to countering the attack, he testified.

Wuterich, who was on his first combat tour, described shooting five men because they were starting to run away.

Sgt. Sanick Dela Cruz, a squadmate, previously testified the men weren't running but were instead "just standing around," some with hands interlocked on their heads.

Dela Cruz testified with immunity after prosecutors dropped murder charges against him. He also said Wuterich had told him to tell anyone who asked that the men had been running away.

Wuterich is also charged with making a false official statement and telling Dela Cruz to do the same.

Wuterich said Thursday he never told Dela Cruz to lie.

He also said he did not stop to check who was in the houses his men cleared.

"I can't remember my exact words, but I wanted them to understand that hesitation to shoot would only result in the four of us being killed," he said.

He said he wasn't required to positively identify his targets before shooting because he had determined the houses were hostile.

Wuterich faces a possible life sentence and dishonorable discharge if court-martialed.

Lt. Col. Paul Ware, the investigating officer overseeing the Haditha case, gave lawyers until Sept. 14 to file any written documents. He will then make a recommendation about whether Wuterich should stand trial.

Lt. Gen. James Mattis, the general overseeing the case, will make the final decision.

Ware has already recommended that charges be dismissed against two other Marines who had been charged with murder in the incident.