Investigators have begun piecing together a harrowing story of missed clues and sudden carnage left by an army psychiatrist who gunned down more than 40 people on a Texas army base, killing 13, when faced with the prospect of deploying to a war he wished President Obama had ended.

At the time, the signs that Major Nidal Malik Hasan was close to breaking point went unnoticed. Hours later they were being logged as evidence in a case that is likely to end in the death penalty for the sole suspect in the worst mass shooting on a US military post in recent history.

The day before Major Hasan smuggled two registered handguns into the Soldier Readiness Processing Centre at Fort Hood and started firing, he had knocked on neighbours’ doors and offered shelves, a lamp and frozen broccoli from a flat to which he did not expect to return.

He also distributed several copies of the Koran, telling one confused recipient that he was moving to Oklahoma and another that he was deploying to Iraq.

The truth was infinitely more troubling. First, he drove on to the sprawling base in central Texas to which he had been assigned in July after a six-year stint at America’s largest hospital for wounded veterans, in Washington.

Wearing a white salmar kameez and cap, he stopped as usual at a convenience store for a breakfast of hash browns and coffee. Closed-circuit television footage aired repeatedly on US news networks yesterday showed Major Hasan’s incongruous and somewhat chubby figure smiling as he pocketed his change and headed for the door.

His workplace was the Darnall Hospital near the southern entrance to Fort Hood, a short drive from his home in neighbouring Killeen.

How much time he spent there was unclear but some time before 1.30pm he made the short journey, a few blocks west, to the building where 300 uniformed personnel were receiving final vaccinations and eyesight checks before being sent overseas.

When he began shooting, the orderly lines of soldiers queuing for treatment dissolved in seconds into bloody chaos.

Witnesses described soldiers tearing off their shirts to staunch the bleeding of those hit in a ten-minute rampage during which Major Hasan may have had time to reload his weapons, and friendly fire may have added to the casualties.

One soldier who was hit in the initial fusillade said: “I made the mistake of moving and I was shot again.”

A female civilian police officer on contract to the US Army, Kimberly Munley, shot Major Hasan four times and was being described as a hero without whom the death toll could have been far higher.

But by the time the gunman was brought down she and more than 40 others had been hit. She and Major Hasan were among the 30 people wounded but in stable condition being treated in military and civilian hospitals throughout the region.

“She happened to encounter the gunman. In an exchange of gunfire she was wounded but managed to wound him four times,” a base spokesman said. “It was an amazing and aggressive performance.”

Sergeant Steve Hagerman, a military police officer and Iraq war veteran, was one of the first on the scene after the shooting.

“You’re always surprised how much carnage there is,” he said, drawing an unconscious parallel between the tragedy on what should have been one of the most secure bases in the US and scenes he had witnessed in Iraq.

A lifelong Muslim, Major Hasan had told colleagues that he was willing to deploy to Afghanistan but not to Iraq. Officials confirmed yesterday that he was due to be sent to Iraq this month, and Lieutenant-General Bob Cone, the base commander, relayed unconfirmed reports that before starting to shoot the gunman had yelled “Allah Akhbar” — “God is great”.

President Obama, in his second set of televised remarks on the massacre, said he had been briefed yesterday morning by the head of the FBI and urged Americans not to rush to judgment as evidence was gathered and associates of the suspect found and interviewed. “We don’t know all the answers yet and I would caution against jumping to conclusions until we have all the facts,” the President said.

He said he had ordered flags on federal buildings to be flown at half-mast nationwide until Veterans’ Day, next Wednesday. Mr Obama is expected to attend a memorial at Fort Hood.

A spokesman for the Hasan family, which has Palestinian roots, called Major Hasan’s actions “despicable and deplorable”. He insisted in a statement that the killings did not reflect the suspect’s upbringing as a US citizen born and raised in Virginia.

In Maryland police were interviewing former colleagues of the gunman at the military university where he studied the effects of traumatic stress on combat veterans, and where he worshipped at a mosque in Silver Spring.

Faizul Khan, a former imam there, said: “I got the impression that he was a committed soldier.”

The American Muslim community distanced itself from the actions of a “rogue” gunman yesterday, drawing attention to the thousands of Muslims “who serve honourably every day in all four branches of the US military”, as the Arab American Institute said.

The full text of posting by Major Nidal Hasan on the “social publishing” site Scribd.com:

“There was a grenade thrown among a group of American soldiers. One of the soldiers, feeling that it was to late for everyone to flee jumped on the grave with the intention of saving his comrades. Indeed he saved them. He inentionally took his life (suicide) for a noble cause i.e. saving the lives of his soldier. To say that this soldier committed suicide is inappropriate. Its more appropriate to say he is a brave hero that sacrificed his life for a more noble cause. Scholars have paralled this to suicide bombers whose intention, by sacrificing their lives, is to help save Muslims by killing enemy soldiers. If one suicide bomber can kill 100 enemy soldiers because they were caught off guard that would be considered a strategic victory. Their intention is not to die because of some despair. The same can be said for the Kamikazees in Japan. They died (via crashing their planes into ships) to kill the enemies for the homeland. You can call them crazy i you want but their act was not one of suicide that is despised by Islam. So the scholars main point is that ‘IT SEEMS AS THOUGH YOUR INTENTION IS THE MAIN ISSUE’ and Allah (SWT) knows best.”

Times Recommends

• 'New York has lost its edge'
• Copenhagen will fail – and quite right too
• More than 17,000 new underwater species found