More than 200 University of Arizona student volunteers helped put together the memorial and unveiled a display holding messages from the public, addressed to victims' families. Obama met with families of the victims shortly before the evening service.
The university's president said that Wednesday is a day for healing, as the entire community tries to come to terms with the tragic shooting.
Off campus, residents attended a special mass Tuesday night at a church just blocks away from where the shooting took place.
It's the same church where 9-year-old Christina Green took her first communion.
Green was among 19 people who were shot in the attack, including U.S. Rep. Gabrielle Giffords.
The accused shooter, Jared Loughner, allegedly unleashed a barrage of bullets at a Saturday campaign event at a Tucson Safeway grocery store. Six people were killed.
Giffords was shot in the forehead during the attack but has been making headway through a difficult recovery process. As of Wednesday, doctors said Giffords is becoming more responsive as she comes off heavy medication. Doctors also said she is making small movements on her own and even tugging at her hospital gown.
She was able to breathe on her own for the first time on Tuesday since the shooting.
Those who know the accused shooter, Jared Loughner, say they're struggling to cope with public scrutiny and media attention.
Family and friends say Loughner's demeanor took a turn for the worse in high school.
"When you see something like this going on, they had nothing to do with this, and I don't know what happened to their son. He was a great kid - just a great kid. Seems like he just snapped somewhere in high school and just went down from there," said Bub Hebert, Lougher's family friend.
As investigators piece together the timeline of the day of the attack, new details are emerging about Loughner's whereabouts and actions.
In the hours before the assassination attempt against Giffords, Loughner was pulled over for running a red light. He was let off with a warning, according to the Arizona Game and Fish Department.
The officer took Loughner's driver's license and vehicle registration information at about 7:30 a.m. but found no outstanding warrants and didn't search the car.
About 8 a.m., Randy Loughner saw his son walk to one of the family's vehicles and take a black bag out of the trunk.
"The father went out and said, 'What's that?' and he mumbled something and took off running," said Sheriff Clarence Dupnik.
Randy Loughner got in his truck and chased his son, but Jared ran into the desert.
Less than two hours later, Lougher carried out the deadly attack.
Hours after the attack, sheriff's deputies swarmed the Loughners' home and removed what they describe as evidence Loughner was targeting Giffords. Among the handwritten notes was one with the words "Die, bitch," which authorities believe was a reference to Giffords.
Loughner's parents released a written statement Tuesday:
"There are no words that can possibly express how we feel. We wish that there were so we could make you feel better. We don't understand why this happened. It may not make any difference but we wish that we could change the heinous events of Saturday. We care very deeply about the victims and their families. We are so very sorry for their loss."
Loughner appeared with a shaved head in a Phoenix federal courtroom for the first time on Monday.
He showed no emotion and only briefly spoke when the judge asked if he understood that he could get life in prison or the death penalty. He replied, "Yes."
Loughner is being held without bail.
The Associated Press contributed to this report.