Centennial, Colorado (CNN) James Eagan Holmes did not start out in this world as a psycho killer. The evidence his lawyers presented in court last week showed he once was a cute, happy little boy from a doting family, a nice kid who was gentle with his dog and his baby sister.

He was wanted, he was encouraged and he was taken to piano lessons and soccer practice and neighborhood birthday parties. He was at the center of a pack of exceptional boys who ruled his Northern California neighborhood and elementary school.

It all seemed so Norman Rockwell normal.

He did well in school and played basketball and video games. He went to the beach, on camping trips in the mountains and to Disneyland. There were family gatherings on Thanksgiving and Christmas and neighborhood parties on July 4 and Halloween.

He was a bit of a prodigy. After he finished his assignments in fifth grade, he and a classmate filled the time writing code and building a website for the school. His teacher, impressed, called him a "Renaissance child."

The 13th Juror With the experienced eye of a trained observer and an avid trial-watcher's curious mind, Ann O'Neill is "The 13th Juror" for CNN's audience. Follow @AnnoCNN on Twitter daily.

By middle school, according to testimony, he was one of the top five players in the world at the video game Warcraft III. He also was starting to withdraw from people. Mental illness was always lurking in the background, Holmes' lawyers say. It stole his childish joy, and ultimately any chance he had for a normal life.

A convicted mass killer, he asked for mercy and didn't get it. Jurors found that the mental illness he indisputably suffers cannot outweigh the horror of 12 murders. And so we move to the third and final phase of his sentencing trial. This time, jurors will hear more heart-rending testimony from the people who survived or lost loved ones.

Holmes will at the very least spend the rest of his days locked up. It is possible he may be put to death.

Mental illness was the reason Holmes opened fire in a crowded movie theater on July 20, 2012, killing 12 people and wounding 70, his lawyers insist. Mental illness turned a smart, shy boy into one of the worst mass shooters in recent U.S. history.

Photos: Colorado shooting victims Photos: Colorado shooting victims Jonathan T. Blunk, 26, served for five years in the U.S. Navy. He died shielding a friend from the gunfire inside the theater. Hide Caption 1 of 12 Photos: Colorado shooting victims Alexander J. Boik, 18, was remembered by friends and loved ones as a "great person" whose "craziness touched hundreds," according to a Facebook page created in his memory. Hide Caption 2 of 12 Photos: Colorado shooting victims Air Force Staff Sgt. Jesse E. Childress, an Air Force reservist, was a cybersystems operator on active duty. He was 29. Hide Caption 3 of 12 Photos: Colorado shooting victims Gordon W. Cowden, 51, took his two teenage children to the theater. His children escaped unharmed. Hide Caption 4 of 12 Photos: Colorado shooting victims Jessica Ghawi, 24, was an aspiring sports reporter. She grew up in Texas before moving to Denver to try break into the television market there. Hide Caption 5 of 12 Photos: Colorado shooting victims Petty Officer 3rd Class John Thomas Larimer, 27, served in the Navy like his father and grandfather. He had been in the service for about a year. Hide Caption 6 of 12 Photos: Colorado shooting victims Matthew R. McQuinn, 27, died trying to provide cover for his girlfriend, Samantha Yowler, during the shooting, according to a family attorney. Yowler survived. Hide Caption 7 of 12 Photos: Colorado shooting victims Micayla C. Medek, 23, known to her friends as Cayla, was "very spiritual and close to God," cousin Anita Busch told CNN. Hide Caption 8 of 12 Photos: Colorado shooting victims Veronica Moser Sullivan, 6, was the youngest victim of the Aurora theater shooting. She had just learned how to swim. Hide Caption 9 of 12 Photos: Colorado shooting victims Alex M. Sullivan, 27, went to the movie to celebrate his birthday with his wife, two days before their first wedding anniversary. Hide Caption 10 of 12 Photos: Colorado shooting victims Alexander C. Teves, 24, recently graduated from the University of Denver with a master's degree in counseling psychology. He died protecting his girlfriend. Hide Caption 11 of 12 Photos: Colorado shooting victims Rebecca Ann Wingo, 32, joined the Air Force after high school, became fluent in Mandarin and served as a translator, according to CNN affiliate WFAA. Hide Caption 12 of 12

Prosecutor George Brauchler argued that mental illness shouldn't be used as a "shield" to protect Holmes from the punishment he deserves for taking so many lives in such a cruel manner. Holmes showed his victims no mercy.

But in the second stage of the sentencing process, the defense commanded center stage. Holmes' lawyers didn't have to prove their points. But they had to persuade at least one juror that sparing his life is the right thing to do. It didn't happen.

Robert, Arlene and Chris Holmes are good people, the defense wants jurors to know, and they will miss their son and brother if he's executed.

This is a textbook capital defense work. It's how attorneys try to save a life. They do everything possible to humanize killers, bringing in people who knew them as innocent children, not monsters. Holmes' lawyers told jurors that if they are to hold his life in their hands, they must know everything about it.

How a boy 'lost his joy'

Photos: Colorado movie theater massacre Photos: Colorado movie theater massacre The public gets its first glimpse of James Holmes, then 24, the suspect in the Colorado theater shooting during his initial court appearance July 23, 2012. With his hair dyed reddish-orange, Holmes, here with public defender Tamara Brady, showed little emotion. He is accused of opening fire in a movie theater July 20, 2012, in Aurora, Colorado, killing 12 people and wounding 70. Holmes faces 166 counts, almost all alleging murder or attempted murder. He has pleaded not guilty by reason of insanity. More photos: Mourning the victims of the Colorado theater massacre Hide Caption 1 of 45 Photos: Colorado movie theater massacre Police release the official photo from Holmes' booking after the shooting. Hide Caption 2 of 45 Photos: Colorado movie theater massacre Holmes often had a blank stare during his July 23, 2012, court appearance, seeming to be in a daze. Hide Caption 3 of 45 Photos: Colorado movie theater massacre Victims and their relatives and journalists watch the proceedings in 2012. Hide Caption 4 of 45 Photos: Colorado movie theater massacre Flags fly at half-staff on July 23, 2012, at the Arapahoe County Courthouse in Centennial, Colorado, where the movie theater shooting suspect had his first court appearance. The murder counts against Holmes carry a possible death penalty. Hide Caption 5 of 45 Photos: Colorado movie theater massacre Arapahoe County District Attorney Carol Chambers talks to reporters July 23, 2012, before heading into the courthouse. The murder counts against Holmes carry a possible death penalty. Hide Caption 6 of 45 Photos: Colorado movie theater massacre Family members of the victims arrive at the courthouse July 23, 2012, for the suspect's first court appearance. Hide Caption 7 of 45 Photos: Colorado movie theater massacre The Century Aurora 16 multiplex in Aurora becomes a place of horror after a gunman opened fire July 20, 2012, in a crowded theater. Hide Caption 8 of 45 Photos: Colorado movie theater massacre Holmes is accused of opening fire during a midnight screening of the Batman movie "The Dark Knight Rises." Holmes purchased four weapons and more than 6,000 rounds of ammunition, police say. Hide Caption 9 of 45 Photos: Colorado movie theater massacre Police investigate outside the Century 16 multiplex July 21, 2012, a day after the mass shooting. Hide Caption 10 of 45 Photos: Colorado movie theater massacre Agents search the suspect's car outside the theater. Hide Caption 11 of 45 Photos: Colorado movie theater massacre Aurora police escort a sand-filled dump truck containing improvised explosive devices removed from Holmes' booby-trapped apartment on July 21, 2012. Authorities have said they believe the suspect rigged his place before leaving for the movie theater. Hide Caption 12 of 45 Photos: Colorado movie theater massacre Police break a window at the suspect's apartment July 20, 2012, in Aurora. Hide Caption 13 of 45 Photos: Colorado movie theater massacre Law enforcement officers speak with Colorado Gov. John Hickenlooper, center, outside the suspect's apartment July 21, 2012. Hide Caption 14 of 45 Photos: Colorado movie theater massacre Law enforcement officers prepare to disarm the booby-trapped apartment July 21, 2012. Hide Caption 15 of 45 Photos: Colorado movie theater massacre Officials tow cars outside Holmes' apartment July 21, 2012. Police disassembled devices and trip wires set up in the apartment. Hide Caption 16 of 45 Photos: Colorado movie theater massacre Officers prepare to place an explosive device inside the apartment. Hide Caption 17 of 45 Photos: Colorado movie theater massacre Debris flies out a window, right, after law enforcement officers detonate an explosive device inside the apartment July 21, 2012. Hide Caption 18 of 45 Photos: Colorado movie theater massacre People mourn the victims during a vigil behind the theater where a gunman opened fire on moviegoers in Aurora. Hide Caption 19 of 45 Photos: Colorado movie theater massacre A woman grieves during a vigil for victims behind the theater. Hide Caption 20 of 45 Photos: Colorado movie theater massacre A distraught woman receives counseling from the Rev. Quincy Shannon, left, in front of Gateway High School in Aurora, where the families of the missing met after the shooting. Hide Caption 21 of 45 Photos: Colorado movie theater massacre Lin Gan of Aurora holds back tears as she speaks to reporters about her experience in the Century 16 theater. Hide Caption 22 of 45 Photos: Colorado movie theater massacre People embrace before a vigil for victims behind the theater where a gunman opened fire on moviegoers. Hide Caption 23 of 45 Photos: Colorado movie theater massacre Investigators work on evidence near the apartment of James Holmes on July 20, 2012. Hide Caption 24 of 45 Photos: Colorado movie theater massacre Members of the Aurora Police Department SWAT unit walk near the Holmes' apartment. Hide Caption 25 of 45 Photos: Colorado movie theater massacre Television news crews gather in front of the home of Robert and Arlene Holmes, parents of suspect James Holmes, in San Diego on July 21, 2012. Hide Caption 26 of 45 Photos: Colorado movie theater massacre A popcorn box lies on the ground outside the Century 16 movie theater. Hide Caption 27 of 45 Photos: Colorado movie theater massacre Adariah Legarreta, 4, is comforted by her grandmother Rita Abeyta near the Century 16 Theater in Aurora. Hide Caption 28 of 45 Photos: Colorado movie theater massacre Jessica Ghawi, an aspiring sportscaster, was one of the victims. Hide Caption 29 of 45 Photos: Colorado movie theater massacre A woman waits for news outside Gateway High School, a few blocks from the scene of the shooting at the Century Aurora 16. Hide Caption 30 of 45 Photos: Colorado movie theater massacre Aurora police chief Daniel J. Oates speaks at a press conference near the Century 16 Theater on July 20, 2012. Hide Caption 31 of 45 Photos: Colorado movie theater massacre Agents search the trash container outside the suspect's apartment in Aurora. Hide Caption 32 of 45 Photos: Colorado movie theater massacre A Federal ATF officer carries protective gear onsite at the home of the shooting suspect. Hide Caption 33 of 45 Photos: Colorado movie theater massacre President Obama speaks on the shootings at a July 20, 2012, event in Fort Myers, Florida. Hide Caption 34 of 45 Photos: Colorado movie theater massacre Moviegoers are interviewed at the Century Aurora 16. Hide Caption 35 of 45 Photos: Colorado movie theater massacre Officers gather at the theater July 20, 2012. Hide Caption 36 of 45 Photos: Colorado movie theater massacre Investigators were a common sight at the theater on July 20, 2012. Hide Caption 37 of 45 Photos: Colorado movie theater massacre Authorities gather at the shooting suspect's apartment building in Aurora. Police broke a second-floor window to look for explosives the suspect claimed were in the apartment. Hide Caption 38 of 45 Photos: Colorado movie theater massacre Screaming, panicked moviegoers scrambled to escape from the black-clad gunman, who wore a gas mask and randomly shot as he walked up the theater's steps, witnesses said. Hide Caption 39 of 45 Photos: Colorado movie theater massacre Onlookers gather outside the Century Aurora 16 theater. Hide Caption 40 of 45 Photos: Colorado movie theater massacre A woman sits on top of her car near the crime scene. Hide Caption 41 of 45 Photos: Colorado movie theater massacre Police block access to the Town Center mall after the shooting. Hide Caption 42 of 45 Photos: Colorado movie theater massacre Cell phone video taken by someone at the theater showed scores of people screaming and fleeing the building. Some, like this man, had blood on their clothes. Hide Caption 43 of 45 Photos: Colorado movie theater massacre Witnesses told KUSA the gunman kicked in an emergency exit door and threw a smoke bomb into the darkened theater before opening fire. Hide Caption 44 of 45 Photos: Colorado movie theater massacre What is believed to be the suspect's car is examined after the shooting. Hide Caption 45 of 45

He was just 24 when he killed the people in the theater. And so, the life story told in court was largely that of a child and teenager.

Screens in the courtroom displayed Holmes' birth announcement -- a boy, 7 pounds, 5 ounces and 20 inches. He was "this miracle," said his mother, Arlene Holmes. It was the first time she'd talked publicly at any length about her son, known to the world as the Aurora movie theater shooter.

His was not a childhood of hardship and neglect. It was a childhood to envy.

"He was planned for and wanted and hoped for and waited for," his mother said. "We wanted a child and had one. It was what we prayed for."

He came into the world inheriting a bundle of family traits. Like his mathematician father, he was quiet, analytical and an academic overachiever. As he grew older, he also shared another trait -- social awkwardness. He inherited his stoicism from his mother, who built a family culture that celebrated hard work and community service and frowned on weakness.

But there was another family trait lurking in the background, and it showed its face as they boy grew into a man. Close relatives, including his father's twin sister, had been institutionalized.

"Mental illness can strike like cancer, without regard to your background, without regard to your status in life, without regard to how intelligent you are," defense attorney Tamara Brady told the jury. "And when James Holmes was born, he had this psychotic mental illness in his blood. It was in his DNA."

He was the first grandchild. And so the jury saw videos with the grandmothers -- sitting in a chair at the kitchen table, getting his first haircut. Standing on tiptoes by the kitchen counter, rolling out dough for gingerbread men. Hugging his baby sister and tentatively tapping out "Jingle Bells" with her at the piano.

The jury saw his baby book, and a family history he put together in elementary school. Then came the report cards -- usually with straight A's -- and a stack of school and team pictures.

His father called him Jimmy, his mother called him Jim and prosecutors disdainfully called him "that guy."

The defense presented three dozen witnesses -- neighbors, family friends, teachers, coaches, friends and classmates -- who described a boy who never picked fights, was never angry and tried his best to blend into the background. He was able to remain invisible for a long time as he battled the demons within.

A traumatic move

His decline began when he was 12 and the family moved from Castroville, near Monterey, to San Diego. He had trouble making friends and began to withdraw into his room and his video games. His mother went door-to-door looking for playmates but, she said, the boys in their new neighborhood weren't very friendly.

She recalled how her boy "lost his joy." She felt guilty that she couldn't make him happy.

Looking back, the defense said, what was chalked up to a tough adjustment was probably an early symptom of Holmes' mental illness. By the time he was in high school, a cross-country coach had taken notice of his behavior. He kept himself apart and was so uncomfortable standing close to others that he wrecked the team photo.

"He was of us, and not of us," the coach said.

His college years were uneventful. He had a handful of friends among the honors students and earned A's at the University of California at Riverside. But he wasn't very outgoing. The social highlight of his week was watching the television show "Lost" with his roommates.

He didn't get into the top graduate schools he applied to, and returned home, where he stayed up late, slept during the day and seemed rudderless until his mother insisted he get a job. He went to work at a pill factory, where co-workers noticed his tendency to stare off into space with an odd, faraway expression.

A second round of grad school applications won him acceptance at the University of Colorado's Anschutz Medical Campus in Aurora, a suburb of Denver. But instead of sailing through his courses with straight A's, Holmes struggled for the first time.

In 2012, he finally came undone, according to the defense. He was dumped by the first girlfriend he'd ever had, and he dropped out of grad school. He was losing the battle with what he called his "broken brain."

The prosecution portrays these setbacks as possible reasons for Holmes to lash out with violence. But the defense says they were merely triggers for psychosis.

He'd come to the conclusion that his broken brain couldn't fix itself, no matter how much neuroscience he studied. He couldn't handle the social interactions required for lab work and presentations.

His attention shifted to planning and carrying out a "mission" to increase his self-worth so he wouldn't have to take his own life, the defense asserts.

In a notebook that he mailed to a psychiatrist, he described a bizarre "human capital" theory, in which he could add value to his own life by taking the lives of others.

'Genetically loaded'

Within moments of hearing her brother had been arrested for the Aurora theater massacre, Chris Holmes knew things would get bad. She knew the police and FBI would invade her home looking for clues. She plucked a photo from a cardboard collage of her life that she'd made in the ninth grade. It was still in her room.

The photo showed Chris with her big brother. They are young and grinning broadly as they floss their teeth. It was a favorite, and she didn't want the authorities to take it from her.

Holmes' mother said she wished the psychiatrist who called her from Denver a month before the theater shootings had told her that he was talking about killing people. She would have dropped everything to rush to his side. "I would have crawled on all fours," she said, breaking into tears.

His father said he thought his son was "an excellent kid." He didn't understand how sick Jimmy was. He worried about him and was planning to take time off from work that August to travel to Denver to check on him. But by then, it was too late.

The family's testimony was heartbreaking, reminding everyone in the courtroom that the ripples of this tragedy extend in all directions.

But it was the expert witness who cut to the core issue. Dr Jeffrey Metzner, a court-appointed forensic psychiatrist, testified that Holmes was "genetically loaded" for mental illness. None of what happened was his choice.

Metzner diagnosed Holmes with schizoaffective disorder, a variety of schizophrenia that combines psychosis, hallucinations and delusions with a mood disorder such as mania or depression.

Defense attorney Tamara Brady told jurors that her client's withdrawn behavior in his early teens was symptomatic of the onset of mental illness. She also pointed out other examples of behavior that at the time was dismissed as shyness, or social awkwardness.

But shy people don't dye their hair orange, as Holmes did before the shooting. They don't talk about "human capital." They don't pose for selfies in black contact lenses and body armor, with guns in their hands.

In March 2012, he finally sought the help of a psychiatrist on campus. He stopped hiding his thoughts and stated that he was thinking about killing people. But a lot of mentally ill people do that, and the psychiatrist saw no evidence he'd actually act on those thoughts. Still, she wondered if he might be psychotic.

Do we execute people who are mentally ill?

Holmes was given medication, including Zoloft, which eased his anxiety, but also may have triggered a mania that led him to purchase guns, ammunition and ballistic gear as he rushed to complete his "mission," Brady said.

About four months after the theater shootings, Holmes had a serious psychotic break in jail. He licked the cell walls, smeared feces and performed somersaults with a paper cup balanced on his penis. He saw shadows and tried to get away from them.

Holmes was and still is severely mentally ill, Metzner testified. But for that mental illness, the shooting rampage at the theater never would have happened.

And so, 60 days of trial boils down to one question: Do we execute people who are mentally ill? How sick does a person have to be to deserve our mercy?

Jurors had the unenviable task of sorting it out. The question before them, as written, posed a logical helix of double negatives:

"Does the jury unanimously find beyond a reasonable doubt that the mitigating factors that exist do not outweigh the aggravating factors proven by the prosecution?"

If the answer was no, the trial would have ended; Holmes would have received a sentence of life in prison.

But the answer was yes,and that means the trial continues to a third phase in which the jury will have to decide between life in prison and the death penalty. This phase will feature shooting survivors and relatives of the dead talking about what they've lost and how their lives have been forever changed.

One last time, the jury will confront this question: Should we execute people who are mentally ill?

"I think Mr. Holmes' actions on July 20 were the direct result of his mental illness," said Metzner. "It all boils down to whether you believe he had a delusion or not."

Holmes' insanity defense already has failed. The jury decided he knew right from wrong when he opened fire in the theater, and so he didn't fit the definition of legal insanity. Jurors found him guilty and agreed prosecutors had proved four aggravating factors -- things that place his crime among the worst:

-- He committed multiple murders.

-- He exposed others to great risk of death.

-- His crimes were especially cruel.

-- And he laid in wait, ambushing his victims.

The defense raised more than 60 mitigating factors for the jury to weigh. It was not clear from their verdict which, if any, the jurors found to be true.

Some were minor, and pale in comparison with the horrors of the crime. But Holmes' mental illness caused those horrors, and they gave him no pleasure, Brady said in a passionate closing argument.

'When does mitigation outweigh aggravation?'

When does mitigation outweigh aggravation? Brady answered her own question: "When the mitigation is the cause of the aggravation. Mental illness caused Jimmy to shoot in that theater."

Prosecutor Brauchler, who presented no evidence during the second phase, urged jurors not to use mental illness as an excuse for Holmes' crimes.

"He made a decision to massacre, and he did," Brauchler said. "Twelve dead from the community. Can anything outweigh that? No. No."

He counted off the victims, showing photos of the "Before" -- happy people enjoying life -- juxtaposed with grisly crime scene photos of the "After" -- bodies crumpled and bloodied, some of them frozen at odd angles as they attempted to escape Holmes' barrage of bullets.

Brauchler's closing argument, already disjointed, was thrown off by a courtroom outburst.

"He's wrong!" a woman shrieked. "Don't kill him! Don't kill him!"

The woman was sitting in the public courtroom seats. Deputies, who had kept an eye on her, moved quickly to eject her. But she could be heard screaming from the hall. It was yet another unsettling event at a trial full of disturbing sights and sounds.

The woman told deputies she was homeless. She seemed to have mental issues, saying she'd been harassed and forced to show identification to get into the courtroom.

In fact, security at the trial is tight, and everyone is screened before entering the courtroom.

The defense suggested it might be more "humane" to hospitalize the woman. But the judge held her in contempt of court and sentenced her to three weeks in jail, saying her actions were "extremely offensive to the authority and dignity of the court."

"It offends me as a human being," she shot back, "that other human beings kill each other legally. You can't justify murder with murder!" she shouted as she was led off to jail.

The outburst seemed to underscore a major theme of the defense case: We as a society aren't good at dealing with the mentally ill.