People have been leaving tributes at a memorial set up behind the cinema where the shootings took place on Friday
In his weekly radio address, he called for prayer and reflection on the gun rampage in the Denver suburb.
Pope Benedict has voiced "deep shock" over the attack which left another 58 people injured, some critically.
The gun suspect, James Holmes, 24, currently being held in solitary confinement for his own safety, is reported not to be co-operating.
Names of the dead
- Jessica Ghawi, 24
- Veronica Moser, 6
- John Larimer, 27
- Alexander Boik, 18
- Jesse Childress, 29
- Jonathan Blunk, 26
- Rebecca Ann Wingo, 32
- Alex Sullivan, 27
- Gordon Cowden, 51
- Micayla Medek, 23
- Alexander Teves, 24
- Matthew McQuinn, 27 (presumptively identified, awaiting confirmation)
People have been laying flowers near the Century cinema.
An evening vigil, organised by local community and religious leaders, is due to take place in front of Aurora city hall later on Sunday.
Colorado governor John Hickenlooper said it was unlikely Mr Obama would stay for the vigil but the president would make a brief speech.
Aurora Mayor Steve Hogan said: "I think the president coming in is a wonderful gesture. He's coming in, really, to have private conversations with the families."
Mr Oates said: "As awful as what they've been through and what they're going through has been, having the president here is very, very powerful."
Both Mr Obama and his Republican Party challenger, Mitt Romney, curtailed their election campaigns in the wake of the Aurora attack, dropping advertising in Colorado state out of respect for victims and their families.
Gun range Mr Obama's visit comes a day after police cleared James Holmes's flat of explosives which could have killed people entering via the door.
The FBI is now collecting evidence from the flat of Mr Holmes, who is accused of at least 12 counts of first-degree murder.
Investigators say a computer found inside his home could provide crucial details.
Police said the suspect had acted with "calculation and deliberation", taking ammunition deliveries for months.
Police chief Oates said: "I've personally never seen anything like what we've found in there."
James Holmes is due to appear in court on Monday.
Authorities have established no terrorism link, nor any motive. Mr Holmes had no criminal record other than a speeding fine.
It has emerged that Mr Holmes tried to join a Colorado gun range last month but owner Glenn Rotkovic told Associated Press he warned staff not to accept him after hearing a "bizarre - guttural, freakish at best" message left by Mr Holmes on his voicemail.
The Arapahoe county coroner Michael Dobersen has released the names of the dead.
He said all the deaths were related to gunshot wounds.
The dead include a six-year-old girl and two US military servicemen.
Mayor Hogan told a memorial service for a young victim on Saturday that the community in Aurora was still reeling from the "unbelievable tragedy".
"But I think, as is evidenced by everyone who is here today, all those who were here yesterday, and all the messages of support that we have received from literally around the world, we can I think now start this process of grieving and healing."