Barack Obama appealed for unity at a memorial service for those attacked in the Arizona shooting rampage and implored a divided America to honour them by becoming a better country.
The US president electrified the crowd by revealing that following his Wednesday hospital visit with Representative Gabrielle Giffords, she had opened her eyes for the first time since being shot point-blank in the head in the assassination attempt last week.
First lady Michelle Obama held hands with Ms Giffords' husband, Mark Kelly, as the news brought a cascade of cheers.
While some have blamed America's overheated political climate and the use of violent imagery in campaigns, Mr Obama conceded that there is no way to know what set off Saturday's shooting rampage that left six people dead, 13 others wounded and the nation shaken.
He tried instead to leave indelible memories of the people who were gunned down and to rally the country to use the moment as a reflection on America's behaviour and compassion.
"I believe we can be better," Mr Obama said to a capacity crowd at the University of Arizona basketball arena - and to countless others watching across America.
"Those who died here, those who saved lives here - they help me believe. We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
Mr Obama said Ms Giffords, known as Gabby, opened her eyes a few minutes after he left her intensive care hospital room at Tucson's University Medical Centre, where some of her colleagues in Congress remained.
"Gabby opened her eyes, so I can tell you: She knows we are here, she knows we love her, and she knows that we are rooting for her through what is undoubtedly going to be a difficult journey," he said.
Three of Ms Giffords' close female friends in Congress were there: House Democratic leader Nancy Pelosi, Representative Debbie Wasserman Schultz and Senator Kirsten Gillibrand.
Ms Giffords is expected to survive, although her condition and the extent of her recovery remain in doubt.
As finger-pointing emerged in Washington and beyond over whether harsh political rhetoric played a role in motivating the attack, Mr Obama sought to calm the rhetoric.
"The forces that divide us are not as strong as those that unite us," he said.
Mr Obama's appeal for unity played out against a deepening political debate.
Earlier, Republican Sarah Palin, criticised for marking Ms Giffords' district and others with the cross-hairs of a gun sight during last autumn's campaign, had taken to Facebook to accuse pundits and journalists of using the attack to incite hatred and violence.
Mr Obama spoke to a crowd of more than 13,000 in the arena and thousands more listened on from an overflow area in the football stadium.
Not far away, at University Medical Centre, Ms Giffords lay fighting for her life. Mr Obama also met with other victims there.
Mr Obama faced the expectation to do more than console, to encourage civility, all without getting overly political in a memorial service.
He challenged Americans to engage in a debate that is worthy of those who died. He tapped into the raging debate about the role of incendiary political speech without dwelling on it.
"Let's remember that it is not because a simple lack of civility caused this tragedy. It did not," the president said.
No matter the cause of the shooting, Mr Obama pleaded for Americans to remain civil now as they debate gun control, mental health services and the motivations of the killer.
"At a time when our discourse has become so sharply polarised - at a time when we are far too eager to lay the blame for all that ails the world at the feet of those who think differently than we do - it's important for us to pause for a moment and make sure that we are talking with each other in a way that heals, not a way that wounds," the president said.
The shooting happened on Saturday as Ms Giffords, a three-term Democrat who represents southern Arizona, was holding a community outreach event in a Tucson shopping centre parking lot.
A gunman shot her in the head and worked his way down the line of people waiting to talk with her, law enforcement officials said.
The attack ended when bystanders tackled the man, Jared Lee Loughner, 22, who is in custody.
Mr Obama's speech, by turns sombre and hopeful, at times took on the tone of an exuberant pep rally as he heralded the men who wrestled the gunman to the ground, the woman who grabbed the shooter's ammunition, the doctors and nurses who treated the injured, the intern who rushed to Ms Giffords' aid.
The crowd erupted in multiple standing ovations as each was singled out for praise. The president ended up speaking for more than half an hour, doubling the expected length of his comments.
After offering personal accounts of every person who died, Mr Obama challenged anyone listening to think of how to honour their memories.
He admonished against any instinct to point blame or to drift into political pettiness or to latch onto simple explanations that may have no merit.
Memories of the six people killed dominated much of Mr Obama's speech. The president, for example, recalled how federal Judge John Roll was on his way from attending Mass when he stopped to say hello to Ms Giffords and was gunned down; Dorothy Morris, shielded by her husband, but killed nonetheless; and Phyllis Schneck, a Republican who liked Ms Giffords, a Democrat, and wanted to know her better.
He spoke at length of nine-year-old Christina Taylor Green, the only girl on her baseball team, who often said she wanted to be the first woman to play in the major leagues.
She had just been elected to the student council at her elementary school and had an emerging interest in public service.
Earlier, details of the attacker's activities ahead of the assassination attempt were disclosed.
Before the Saturday shooting, Loughner went shopping at a megastore, was pulled over for running a red light and ran from his father after an angry confrontation
After two shopping trips to Walmart, Loughner ran a red light but was let off with a warning, the Arizona Game and Fish Department said.
The officer took Loughner's driver's licence and vehicle registration information but found no outstanding warrants and did not search the car.
Earlier that morning, a mumbling Loughner ran into the desert near his home after his father asked him why he was removing a black bag from the trunk of a family car, sheriff's officials said.
He resurfaced later Saturday at a grocery store where Ms Giffords was holding an event. There, authorities say, he shot 19 people.
Police records at Pima Community College in Tucson released Wednesday detailed Loughner's increasingly bizarre behaviour last year, culminating with his suspension in September.
The 51 pages of campus police reports, obtained under an open records request, described a series of classroom outbursts and confrontations that prompted worried instructors to summon campus officers.
In a poetry class, he made comments about abortion, wars and killing people, then asked: "Why don't we just strap bombs to babies?"
Police previously said they also found notes with the words "Die, bitch", which they believe referenced Ms Giffords, and "Die, cops."