A jury of US military officers retired Thursday to consider its verdict in the court martial of a comrade who confessed to gunning down 13 soldiers at a Texas base.

The accused, Major Nidal Hasan, who conducted his own defense, gave no closing argument in his capital murder case. If convicted the 42-year-old army psychiatrist could be given a death sentence.

"The defense chooses to give no closing statement," Hasan said, after the prosecution summed up the evidence for the Fort Hood shooting of almost four years ago.

Hasan has admitted carrying out the attack, declaring that he shot fellow American soldiers to prevent them taking part in what he regards as an illegal war against his fellow Muslims in Afghanistan.

Colonel Steven Henricks said Hasan had thought he had a "jihad duty to kill" as many soldiers on November 5, 2009.

He is charged with 45 counts of premeditated and attempted premeditated murder.

"The accused went out that day with the intent to shoot as many soldiers as he could or anyone who would stop him," Henricks said.

On Wednesday, Hasan closed his case without calling a single witness or testifying himself.

But he did say Wednesday that US military action in Afghanistan and Iraq was "illegal."

"These were deploying soldiers that would engage in an illegal war," he said.

Hasan had learned three weeks prior to the shooting that he had been selected for deployment to Afghanistan.

The court heard that in the months leading up to the attack, he had contact with Al-Qaeda figure Anwar al-Awlaki, seeking spiritual guidance on whether attacking soldiers who would kill Muslims was permissible.