The president, appearing drained and solemn following his nearly 3-hour stay, spoke to reporters at the University of Colorado hospital where he visited with the families "not as a president but as a husband and a father."
"I had a chance to visit with each family and most of the conversations were filled with memory," he said. "It was an opportunity for each family to say how wonderful their son or daughter or brother was ... . I expressed to them that words are always inadequate ...but my main task is to let them know that ... we are thinking about them and we will continue to think about them each day. The awareness that not only America but the rest of the world is thinking about them might have some comfort.
"I also tried to assure them that although the perpetrator is receiving a lot of attention, that attention will fade away.
"I also had a chance to give folks some hugs, and to shed some tears but also to share some laughs as they remembered the wonderful lives that these wonderful people represented."
Obama recounted the experience of one of the dozens of those wounded, Allie Young, 19, who was saved by her best friend Stephanie Davies, 21.
He said when the gunman walked in and threw the teargas canisters near the two young women, Young stood up and was immediately shot in the neck and "immediately started spurting blood."
Davies dropped down and pulled her out of the aisle and placed her finger on the wound, staying with her friend despite Young telling her she needed to run, Obama said.
Davies "refused to go," the president said, and dialed 911 with her other hand. After police arrived, Davies helped carry Young to an ambulance.
"Because of Stephanie's timely actions, I just had a conversation with Allie and she's going to be fine," Obama said.
"I don't know how many people of any age would have the presence of mind to do what Stephanie did."
The two friends, Obama said, "represent the best in us."
Obama later headed off later for a campaign event in San Francisco.
Meanwhile, the Aurora police chief said accused theater gunman James Holmes was acting alone when he plotted and carried out his shooting spree.
Chief Daniel Oates denied media reports detectives were seeking a second person of interest in their investigation into the slayings of a dozen people at an Aurora movie theater during a midnight showing of the new Batman film.
"All the evidence we have, every single indicator, is that ... this is all Mr. Holmes' activity and that he wasn't particularly aided by anyone else," Oates said on CBS' "Face the Nation."
"We're building a case to show that this was a deliberative process by a very intelligent man who wanted to do this."
Aurora police and federal agents continued searching the one-time grad student's small apartment for evidence. Investigators were able to enter only after a bomb squad cleared the residence of multiple booby traps.
Oates said Saturday Holmes had been purchasing ammunition and explosives to booby-trap his apartment for almost four months. "What we're seeing here is evidence of, I think, some calculation and deliberation," he told reporters.
Holmes, 24, spent Sunday in the Aurora jail awaiting his initial court appearance Monday.
Holmes' alleged motive in the slayings remained unclear.
A video has surfaced in which Holmes discusses his interest in a neuroscience phenomenon related to time, ABC News said Sunday.
ABC said the video it had obtained was recorded six years ago at a college science camp in his native San Diego and features an 18-year-old Holmes talking about research into "temporal illusion."
"Over the course of the summer I've been working with a temporal illusion," Holmes says in the video. "It's an illusion that allows you to change the past."
Holmes apparently did not get into much detail on temporal illusions, which are related to the perception of time.
He did, however, say he had a mentor who was also interested in the topic. "He also studies subjective experience which is what takes places inside the mind as opposed to the external world," he said. "I've carried on his work in dealing with subjective experience."