FORT HOOD, Texas - Somberly reciting 13 names and 13 stories, President Barack Obama saluted the Americans killed at this Army post as heroes who died for their country - and promised a nation demanding answers that "the killer will be met with justice."

Addressing a hushed crowd of thousands of soldiers Tuesday, the president spoke forcefully if indirectly of the alleged shooter's motives in last week's massacre, never mentioning Maj. Nidal Hasan by name.

"It may be hard to comprehend the twisted logic that led to this tragedy," Obama said. "But this much we do know: No faith justifies these murderous and craven acts."

It was an apparent reference to reports that Hasan had communicated with a radical Islamic imam. A vast investigation is under way, including questions about what the government knew about Hasan and whether action should have been taken.

The president's remarks at a memorial service were personal, more about how the victims lived than how they died: the Eagle scout, the newlywed, the expectant mother, the soldier eager to catch Osama bin Laden by herself. The president spent more time meeting privately with the wounded and with loved ones of those killed than speaking in public.

His tone stern, Obama pledged to the crowd that "the killer will be met with justice - in this world, and the next."

On a steamy Texas day, Obama stepped into a scene filled with military resolve and tender moments. Soldiers helped wounded friends to their seats. A little girl in a black dress and shiny shoes clutched her mother's hand as hurting families streamed in.

Thousands upon thousands gathered on a field for the ceremony. Right below the stage was a traditional military tribute to the fallen - 13 pairs of combat boots, each with an inverted rifle topped with a helmet. A picture of each person rested below the boots.

Riflemen fired a last salute. A bugler played taps.

After the ceremony, Obama walked solemnly along the row of boots, placing a commander-in-chief's coin next to each victim's photo in tribute.

Then soldiers and loved ones traced the same path to remember those lost and give a final salute, one woman nearly collapsing with grief.

Even as Obama honored the dead, there was fingerpointing back in Washington about what the military knew of Hasan, an Army psychiatrist, before the shooting rampage.

Two U.S. officials said a Washington-based joint terrorism task force overseen by the FBI was notified of communications between Hasan and a radical imam overseas and the information was turned over to a Defense Criminal Investigative Service employee assigned to the group. But a military official denied prior knowledge of the Army psychiatrist's contacts with any Muslim extremists.

All of the officials spoke on condition of anonymity because they were not authorized to talk about the case on the record.

In Texas, one soldier who attended the memorial said the mood at Fort Hood was turning from sadness to anger as soldiers learned more about Hasan's background.

"A lot of folks are angry because they feel this could have been prevented," said Spc. Brian Hill, a 25-year-old soldier from Nashville, Tenn., who was injured in Iraq and walks with a cane. "Somebody should have been paying attention."

Obama, in his public remarks, spoke of the tranquility and liberty enjoyed by most Americans, and said the 13 fallen gave their lives for it.

"That is their legacy," he said.

As much as the president made the moment about the gunman's victims, the ceremony also was about him. Presidents inevitably must take the lead in times of tragedy, and this was Obama's moment to offer himself as consoler in chief.

The president worked through several drafts of his speech, including three on the Air Force One flight down to Texas. He viewed the personal stories as the most important part of the speech, a senior aide said.

About the victims and the soldiers who rushed to help them, Obama said, "We need not look to the past for greatness, because it is before our very eyes."

Obama and first lady Michelle Obama devoted considerable time to three private meetings with those affected by the shooting rampage, meeting first with families of those killed, then with some of those wounded and their families, and later with those still hospitalized.

"Just the president being here was a great morale booster to show the country he was here for the families," said Ronald Fiveash, a sailor whose brother was shot four times but survived.

Sheila Wormuth, whose husband is stationed at Fort Hood, came with her 3-year-old daughter to show their support. While her husband wasn't at the shooting site, she said, "what happens to my husband's brothers and sisters happens to us."

Bonita Childs, 46, drove 30 miles to attend the ceremony, even though she had no connection to Fort Hood.

"I thought coming here today and showing my gratitude was the least I could do," she said.

In a memorial offered in deeply personal terms, Obama spoke every victim's name and told of their lives.

"These men and women came from all parts of the country," Obama said. "Some had long careers in the military. Some had signed up to serve in the shadow of 9/11. Some had known intense combat in Iraq and Afghanistan, and some cared for those did. Their lives speak to the strength, the dignity and the decency of those who serve, and that is how they will be remembered."