AURORA, Colo. – Police say they believe the suspect in a deadly shooting at a Colorado movie theater planned the attack with "calculation and deliberation," as they removed all explosives from his booby trapped apartment.
The suspect, James Holmes, is accused of going on a shooting rampage at the movie theater during Friday's midnight showing of "The Dark Knight Rises," killing 12 people dead and injuring 58. He was packing as many as 6,000 rounds of ammunition with the ability to shoot up to 50 a minute, police said.
Meanwhile, a federal source law enforcement official told The Associated Press late Saturday that a semi-automatic assault rifle used by the shooter jammed during the attack, forcing him to switch to another weapon.
The official, who spoke on condition of anonymity to in order to discuss the investigation, said that the jammed weapon had a high-capacity ammunition magazine.
Also late Saturday, the Aurora Police Department dismissed reports a second individual was being looked at as a person of interest or a suspect in the shooting.
In a statement obtained by Fox News, Aurora Police Department spokeswoman Cassidee Carlson called reports of a second suspect "unconfirmed and inaccurate."
She confirmed an "associate" of Holmes had been interviewed in relation to the case, but said at this time they do not believe he was involved.
Sources told Fox News a possible second person of interest in the case was being investigated, though authorities were not yet sure if the individual is necessarily tied to the crime.
The person who owns the home where the reported person of interest lives tells FoxNews.com investigators are looking for his tenant because they have interviewed all students from Holmes's program and his tenant is the only one who they haven't been able to reach. However, the landlord said he believes the tenant has been in Korea for "weeks."
Earlier Saturday, authorities eliminated all the explosives in Holmes' booby-trapped apartment. No officials were injured in the process, but Carlson says the booby trap trip wire at his apartment was "meant to kill," the first person who opened the door to the apartment.
The Aurora police chief says the trap was meant specifically to kill a police officer who might have opened the door.
"We sure as hell are angry," Chief Dan Oates said about the trap being aimed at officers. Oates also apparently tried to head off a mental incompetence defense by saying Holmes was deliberate and calculating in receiving numerous commercial deliveries to his home and workplaces over the past four months.
"This is some serious stuff that our team is dealing with," Sgt. Carlson said. Witnesses have reported hearing two small booms during the disarming process.
Holmes' apartment was loaded with explosives and authorities say they will not know for sure what is inside until they enter and test results come back from an FBI lab. A robot was sent in to disarm and diffuse the major threats as well as remove evidence.
While authorities continued to refuse to discuss a possible motive for one of the deadliest mass shootings in recent U.S. history, details about Holmes' background as a student and would-be scientist trickled out Saturday.
Holmes had recently withdrawn from a competitive graduate program in neuroscience at the University of Colorado-Denver, where he was one of six students at the school to get National Institutes of Health grant money. He recently took an intense three-part, oral exam that marks the end of the first year of the four-year program there, but university officials would not say if he passed, citing privacy concerns. The university said Holmes gave no reason for his withdrawal, a decision he made in June.
"The focus of the program is on training outstanding neuroscientists and academicians who will make significant contributions to neurobiology," the university said. The doctoral program usually takes five to seven years to complete, it said.
In a resume posted on Monster.com, Holmes listed himself as an "aspiring scientist" and said he was looking for a job as a laboratory technician.
The resume, first obtained by The Press-Enterprise in Riverside, paints a picture of a brilliant young man brimming with potential: He worked as a summer intern at the Salk Institute for Biological Studies in La Jolla in 2006 and mapped the neurons of Zebra finches and studied the flight muscles of hummingbirds while an undergraduate at the University of California, Riverside.
He also worked as a cabin counselor to underprivileged children at a summer camp in Los Angeles in 2008. In a statement, Camp Max Straus confirmed Holmes had worked there for eight weeks. The camp provided no other detail about Holmes but said such counselors are generally responsible for the care and guidance of roughly 10 children.
Neighbors and former classmates in California said although Holmes was whip-smart, he was a loner who said little and was easily forgotten -- until this week.
Mary Muscari, a criminology professor at Regis University in Denver who studies mass killings, said she was not surprised Holmes was studying neuroscience and mental disorders.
"It could be he was interested in that because he knows there's something different in him," she said.
Holmes was in solitary confinement for his protection at a county detention facility Saturday, held without bond on suspicion of multiple counts of first-degree murder. He was set for an initial hearing on Monday and has been appointed a public defender.
Among the deceased victims was a 6-year-old girl and a man who died on his 27th birthday and a day before his wedding anniversary. Families grieved and waited at hospitals, which reported at least seven still in critical condition Saturday and others with injuries that likely are permanent.
Veronica Moser-Sullivan, 6, had gone to the movies with her mother, who was drifting in and out of consciousness in a hospital intensive care unit, bullets lodged in her throat and a gunshot wound to her abdomen.
"Nobody can tell her about it," Annie Dalton said of her niece, Ashley Moser. "She is in critical condition, but all she's asking about is her daughter."
Veronica had just started swimming lessons on Tuesday, Dalton said.
"She was excited about life as she should be. She's a 6-year-old girl," her great aunt said.
Another victim, 27-year-old Matt McQuinn, was killed after diving in front of his girlfriend and her older brother to shield them from the gunfire, said his family's attorney, Rob Scott of Dayton, Ohio.
Alex Sullivan had planned a weekend of fun, first ringing in his 27th birthday with friends at the special midnight showing of "The Dark Knight Rises" and then celebrating his first wedding anniversary on Sunday.
"He was a very, very good young man," said Sullivan's uncle, Joe Loewenguth. "He always had a smile, always made you laugh. He had a little bit of comic in him."
President Obama, who called in his weekly radio address for prayer and reflection on the rampage, was scheduled to travel to Colorado on Sunday to visit with the families of victims.
During the attack early Friday, Oates said Holmes used a military-style semi-automatic rifle, a shotgun and a pistol to open fire on the unsuspecting theater-goers. He had bought the weapons at local gun stores within the last two months. He recently purchased 6,000 rounds of ammunition over the Internet, the chief said.
Holmes also bought an urban assault vest, two magazine holders and a knife for just over $300 on July 2 from an online supplier of tactical gear for police and military personnel, according to the company.
Chad Weinman, CEO of TacticalGear.com, said his company processes thousands of orders each day, and there was nothing unusual in the one that Holmes placed.
"Everything Mr. Holmes purchased on July 2 is commercially available," Weinman said, adding he was "appalled" that the material was sold to Holmes before the shooting.
The Batman movie, the last in the trilogy starring Christian Bale, opened worldwide Friday with midnight showings in the U.S. "The Dark Knight Rises" earned $30.6 million in Friday morning midnight screenings and according to industry estimates roughly $75 million on that day. That put it on track for a weekend total of around $165 million, which would be the second-highest opening weekend ever, following "The Avengers."
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.
Fox News' Adam Housley and The Associated Press contributed to this report.