Officials at the University of Colorado Anschutz Medical Campus were looking into whether Holmes used his position in a graduate program to collect hazardous materials, but that disclosure was one of the few it has made three days after the massacre. It remained unclear whether Holmes' professors and other students at his 35-student Ph.D. program noticed anything unusual about his behavior.
His reasons for quitting the program in June also remained a mystery. Holmes recently took an intense oral exam that marks the end of the first year. University officials would not say if he passed, citing privacy concerns.
Amid the continuing investigation of Holmes and his background, Sunday was a day for healing and remembrance in Aurora, with the community holding a prayer vigil and President Barack Obama arriving to visit with families of the victims.
Obama said he told the families that "all of America and much of the world is thinking about them." He met with them at the University of Colorado Hospital in Aurora, which treated 23 of the people injured in the mass shooting; 10 remain there, seven hurt critically.
Congregations across Colorado prayed for the shooting victims and their relatives. Elderly churchgoers at an aging Presbyterian church within walking distance near Holmes' apartment joined in prayer, though none had ever met him.
Several thousand gathered for healing at the vigil Sunday night.
"You're not alone, and you will get through it," said the Rev. Kenneth Berve, pastor at Grant Avenue United Methodist Church and a witness to Friday's horrors. "We can't let fear and anger take control of us."
Meanwhile, the owner of a gun range told the AP that Holmes applied to join the club last month but never became a member because of his behavior and a "bizarre" message on his voicemail.
Holmes emailed an application to join the Lead Valley Range in Byers on June 25 in which he said he was not a user of illegal drugs or a convicted felon, said owner Glenn Rotkovich. When Rotkovich called to invite him to a mandatory orientation the following week, Rotkovich said he heard a message on Holmes' voicemail that was "bizarre — guttural, freakish at best."
Rotkovich left two other messages but eventually told his staff to watch out for Holmes at the July 1 orientation and not to accept him into the club, Rotkovich said.
The pastor for the suspect's family recalled a shy boy who was driven to succeed academically.
"He wasn't an extrovert at all. If there was any conversation, it would be because I initiated it, not because he did," said Jerald Borgie, senior pastor of Penasquitos Lutheran Church. Borgie said he never saw the suspect mingle with others his age at church. He last spoke with Holmes about six years ago.
"He had some goals. He wanted to succeed, he wanted to go out, and he wanted to be the best," Borgie said. "He took pride in his academic abilities. A good student. He didn't brag about it."
During the attack early Friday, Holmes allegedly set off gas canisters and used a semiautomatic rifle, a shotgun and a pistol to open fire on theater-goers, Aurora Police Chief Dan Oates said.
Holmes had bought the weapons at local gun stores in the past two months. He recently bought 6,000 rounds of ammunition over the Internet, the chief said.
The gunman's semiautomatic assault rifle jammed during the attack, forcing him to switch to another gun with less firepower, a federal law enforcement official told The Associated Press. That malfunction and weapons switch might have saved some lives.
Oates said a 100-round ammunition drum was found in the theater, but he said he didn't know whether it jammed or emptied.
The shooting was the worst in the U.S. since the Nov. 5, 2009, attack at Fort Hood, Texas. An Army psychiatrist was charged with killing 13 soldiers and civilians and wounding more than two dozen others.