FORT HOOD, Texas — Sketching out lives that ended too soon, President Barack Obama remembered those slain at Fort Hood — including Utahn Aaron Nemelka — as husbands and fathers, immigrants and scholars, optimists and patriots — an expectant mother, a granddaughter of veterans, a music teacher.

Just below his speaking platform Tuesday, before thousands of mourners, the dead were remembered in a traditional Army way: 13 pairs of combat boots, each with an inverted rifle topped with a helmet. A picture of each person rested below the boots.

"Neither this country, nor the values that we were founded upon, could exist without men and women like these 13 Americans," Obama told the throng. "And that is why we must pay tribute to their stories."

Obama had words, as well, for a nation demanding answers for last Friday's massacre at this Texas Army post. He spoke forcefully if indirectly of the alleged shooter's motives, 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.

"Pfc. Aaron Nemelka was an Eagle Scout who just recently signed up to do one of the most dangerous jobs in the service — defuse bombs — so that he could help save lives. He was proudly carrying on a tradition of military service that runs deep within his family," Obama said.

He talked about Pvt. Michael Pearson's love of music, Maj. Eduardo Caraveo's journey to America as a teenager, Pvt. Francheska Velkez's excitement about becoming a mother, Capt. John Gaffaney's two decades as a psychiatric nurse — and so on through the honor roll of 10 men, three women.

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.