Before he walked into the Batman movie early Friday in Aurora, Colo., dressed head to foot in black body armor and carrying a handgun, a shotgun and an assault rifle, James Holmes was a graduate student in neuroscience, a doctoral candidate who sat in classes with titles such as "Biological Basis of Psychiatric and Neurological Disorders."

He was known as introverted but pleasant. Holmes, 24, had shown scholarly promise in the recent past. He'd earned a merit scholarship out of high school in a San Diego suburb. He had graduated from college with honors. From there, he'd gone to graduate school at the University of Colorado, Denver.

And then something changed. By this spring, Holmes had begun to struggle with poor test scores. He eventually decided to quit school.

What happened next remains a mystery.

As of Friday evening, no one had emerged to speak on Holmes' behalf. He will appear in court Monday and is expected to be formally charged in days.

What's certain is that the killer carefully planned his crime, gearing up as if he were a commando, or a bad guy in a movie, before invading Theater 9 in the Century 16 Movie Theater complex in Aurora during a screening of "The Dark Knight Rises."

The shooter wore a ballistic helmet, ballistic vest, ballistic leggings, a throat protector, a groin protector, gloves and a gas mask, all black. Police say the gunman killed at least 12 people and left 58 others injured, many critically with gunshot wounds, before surrendering meekly when police confronted him at his car behind the theater.

Police would not discuss any motive for the massacre. They said Holmes revealed to them during questioning that he had booby-trapped his Aurora apartment with explosives.

There, police found jars of chemicals with wires nearby, said a law-enforcement official speaking on condition of anonymity.

"Top of the top" in academics

Neighbors in the well-tended San Diego neighborhood of Torrey Highlands recalled him as a clean-cut, studious young man of sparing words.

He stared clear-eyed at the camera in a 2004 high-school yearbook snapshot, wearing a white junior varsity soccer uniform — No. 16. He is the son of a nurse, Arlene, and a software-company manager, Robert.

In the age of widespread social media, no trace of Holmes could be found on Facebook, LinkedIn, MySpace, Twitter or anywhere on the Web. Either he never engaged, or he scrubbed his trail.

A longtime neighbor in San Diego remembered only a "shy guy ... a loner" from a churchgoing family. In addition to playing soccer at Westview High School, he ran cross country.

Holmes struggled to find work after graduating with highest honors in spring 2010 with a neuroscience degree from the University of California, Riverside, said the neighbor, retired electrical engineer Tom Mai.

Holmes enrolled last year in the neuroscience doctoral program at the University of Colorado, Denver, but was in the process of withdrawing, said school officials.

In academic achievement "he was at the top of the top," recalled Riverside Chancellor Timothy White.

Holmes concentrated his study on "how we all behave," White added. "It's ironic and sad."

Not even a traffic ticket

Holmes is not talking to police and has asked for a lawyer, according to the law-enforcement official.

"Our hearts go out to those who were involved in this tragedy and to the families and friends of those involved," Holmes' family said in a written statement Friday. "We ask that the media respect our privacy during this difficult time."

On Friday morning, police escorted the suspect's father from the family's San Diego home. The mother stayed inside, receiving visitors who came to offer support.

San Diego Superior Court spokeswoman Karen Dalton said there were no records found under his name, not even for a traffic ticket. Riverside County prosecutors also have no criminal record for him, said John Hall, a spokesman for the district attorney's office.

Holmes kept a low profile while living in an apartment building near the University of Colorado, Denver, medical campus. Neighbors said they didn't know him. On Friday, graduate students in the university's neurosciences program gathered for a meeting with faculty to discuss Holmes' arrest.

A neuroscience faculty member, who spoke on condition of anonymity, described Holmes as "very quiet, strangely quiet in class," and said he seemed "socially off." Although Holmes got weak scores on the comprehensive exams last semester, the educator said, the school's staff wasn't going to toss him out.

Instead, school officials planned to give him remedial instruction and perhaps put him on academic probation.

Sharing a drink

Jackie Mitchell, a furniture mover who lives several blocks from Holmes' apartment, said he had drinks with Holmes at a local bar on Tuesday night, though he gave no sign of being distressed or violent.

After Holmes approached him "we just talked about football. He had a backpack and geeky glasses and seemed like a real intelligent guy, and I figured he was one of the college students," Mitchell said.

When Mitchell saw Holmes' photo after the shooting, "the hair stood up on my back," he said. "I know this guy."

Material from The Associated Press is included in this report.