Dwarfed by a wall of steel containers and watched by troops around the world, President Obama addressed thousands of mourners yesterday at a memorial service for victims of last week’s “murderous and craven” massacre at Fort Hood, Texas.

In an address crafted to articulate the shock of the US military and his commitment as its Commander-in-Chief, Mr Obama paid tribute in turn to each of the dead and hailed their courage in the defence of timeless American ideals.

“These are trying times for our country,” he said, invoking the memory of the victims of the September 11, 2001, attacks as well as the continuing war in Afghanistan. By answering the call to meet such challenges, he said, those killed last week “remind us of who we are as Americans”.

Facing a sea of soldiers in black berets and fatigues, Mr Obama continued: “We are a nation of laws whose commitment to justice is so enduring that we would treat a gunman and give him due process, just as surely as we will see that he pays for his crimes. We are a nation that guarantees the freedom to worship as one chooses. And instead of claiming God for our side, we remember Lincoln’s words, and always pray to be on the side of God.”

The President flew to Texas as head of the world’s most powerful military, but in the dark suit of a civilian. Accompanied by the First Lady, he expected “an accounting” for any missed signs that Major Nidal Malik Hasan, the sole suspect in the case, was a murderer-in-waiting, his press secretary said. Hours earlier officials admitted that the FBI had intercepted up to 20 e-mails from Major Hasan to a radical cleric, Anwar al-Awlaki, as part of a counter-terrorism operation but had not pursued the lead.

Concerns were also raised and ignored after Major Hasan gave a bizarre, hour-long address to fellow army doctors in 2007 on Muslims in the US military. The presentation, which was supposed to be on a medical topic, included extensive proselytising and a warning of “adverse events” if Muslim soldiers were forced to deploy to war zones.

In an interview before his flight to Texas, Mr Obama acknowledged that the FBI’s task was to establish whether last Thursday’s carnage was the work of a lone gunman or “some larger set of actors”. His own task yesterday was to find words to honour the grief of a 70,000-strong military community and to persuade a much larger audience of the sincerity of his admiration for the military in a time of war.

He was greeted at the massive headquarters building of the US Army’s III Corps by thousands of soldiers, a square of reserved seating for the bereaved and 13 army helmets balanced on semi-automatic rifles, next to 13 pairs of boots. Before leading the memorial service, he spent more than an hour in private with the families of the dead.

Mr Obama had faced criticism for the tone of his initial response to the shooting, given in the midst of congratulatory remarks at a conference of Native Americans in Washington.

George Bush, his predecessor, made a brief, low-key visit to Fort Hood the day after the shootings from his country home in Crawford, Texas. Mr Obama waited five days before paying his respects in person. The trip has delayed by a day his departure on a long-planned tour of Asia, reflecting the importance his aides attach to showing that he can grasp what one former press secretary to President Bush called yesterday “a national moment”.

More than 3,000 mourners gathered to listen to him in the lee of a giant, L-shaped security wall of freight containers usually used to ship military materiel to and from war zones. As they did so, Major Hasan was recovering from multiple gunshot wounds in the nearby Brooke Army Medical Centre at Fort Sam Houston. He was in critical but stable condition and talking — but only through his military lawyer, retired Colonel John Galligan, who said that his client was “coherent” and “aware that he’s a suspect”.

In a deal struck by the Pentagon and the Department of Justice, Major Hasan will be tried by a court martial even though he could have faced a civilian trial under federal terrorism laws if the killings were deemed acts of terror. In either case the death penalty is the most likely outcome.

Intelligence officials said that the FBI alerted the army to Major Hasan’s e-mails to Mr al-Awlaki — an American-born cleric who moved to Yemen after 9/11 — but did not launch an investigation of its own, deciding that the correspondence was consistent with the doctor’s academic interest in Muslims in the military.

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