On the morning of January 29, 1979, teenager Brenda Spencer took a break from shooting people through her window to answer the phone. On the other end was a reporter from the San Diego Tribune. He asked a few short questions to confirm that the young girl was indeed the culprit. “Yeah,” Spencer said. “Who do you think’s doing the shooting?”

The reporter then asked “Why?” and the answer Spencer gave would become famous. “I don’t like Mondays,” she said. “This livens up the day.”

“I have to go now,” she added. “I shot a pig [a policeman], I think, and I want to shoot more.” By the end of her sniping assault, 16-year-old Brenda Spencer had shot 11 people. Eight children and a police officer were injured, and two men — custodian Michael Suchar and principal Burton Wragg — were killed in what is considered the first modern school shooting in the United States.

That morning, Spencer had told her father she was too ill to attend class. Her dad left the house around 7 a.m. Around 8:30 that morning, Spencer retrieved her .22 caliber rifle, equipped with a telescopic sight, and began firing across the street.

Her targets were children. They were gathered outside in the parking lot of Grover Cleveland Elementary, about 150 feet away, waiting to be let into school. The first person Spencer hit was 9-year-old Monica Selvig, who was struck in the wrist by a bullet.

Spencer continued to shoot at the students. “It was fun to watch the children that had red and blue ski jackets on, as they made perfect targets,” she later said to a police investigator. Principal Burton Wragg rushed over to the children, many of whom were paralyzed in place by fear, to guide them to safety. As he tried to help, he was shot in the chest and killed.

Custodian Michael Suchar, a World War II veteran, was killed as he tried to drag Wragg’s body away from the gunfire. Among those injured were 9-year-old Cam Miller, who was shot in the chest, an inch from his heart, and police officer Robert Robb, who was shot in the neck.

Spencer’s assault lasted 15 minutes, before a police officer and a security guard risked their lives to drive a garbage truck in front of Spencer’s house, blocking her line of sight — and attack. After a nearly seven-hour SWAT negotiation, Spencer left her house, surrendered, and was arrested.

The community and country were shocked to see this teenage girl with long wavy hair and large glasses as the source of such evil. Compounding their revulsion was her lack of repentance. “It was a lot of fun seeing children shot,” she told law enforcement, admitting how she “liked to watch them squirm around after.”

Law enforcement investigations uncovered wave after wave of disturbing information. It was learned that Spencer’s father gave her the rifle and 400 rounds of ammunition as a Christmas gift, none of which she requested. “I asked for a radio and he bought me a gun,” Spencer reflected. Even more startling was news that the week before the shooting, Spencer told classmates she was about “to do something big to get on TV.”

What emerged was a portrait of a neglectful and unhealthy home. Spencer’s parents had divorced seven years earlier, and she lived with her father in a home littered with beer and whiskey bottles. Character witnesses remarked that Spencer would often talk about guns, and that she would shoot at cans and birds for fun. Testimony also showed that Brenda and her father slept on the same mattress on the floor.

After her case was moved to Orange County to keep it from becoming a spectacle, Brenda Spencer pleaded guilty in court and was sentenced to 25 years to life.

The summer of that year, Irish rock band The Boomtown Rats released their song “I Don’t Like Mondays,” inspired by the shooting. With lyrics like “And he can see no reasons / because there are no reasons,” it topped the U.K. charts for four straight weeks.

Spencer’s story struck a chord with Irish rockers The Boomtown Rats.

The following few years would provide an abundance of conflicting reports. Law enforcement toxicology tests showed no sign of intoxicants in either Spencer’s blood or urine. Though in a 1993 interview, Spencer claimed that the morning of her attack she had drunk whiskey, smoked marijuana, taken PCP, and had hallucinatory visions of commandos outside her window in combat gear.

In a 2001 parole hearing, Spencer also revealed that her father subjected her to regular sexual assault. Lawyers and state officials were skeptical, feeling if these allegations were true, they would have likely come out 20 years before.

Even Spencer’s self-inflicted scars became matters of interpretation. After a prison breakup, she heated a paperclip to engrave the words “pride” and “courage” into her chest, but when pressed about their significance, she insisted she wrote in runes the words “unforgiven” and “alone.”

At her 2001 hearing, Spencer also, for the first time, expressed public remorse for her actions. She apologized to her many victims, as well as to the inadvertent legacy she left behind. “With every school shooting, I feel I’m partially responsible,” she said. “What if they got the idea from what I did?”

Distancing herself from her actions, she also claims to have no memory of the event.

Spencer was denied parole at her most recent hearing in 2009. She is scheduled for another in 2019.

This article was corrected to reflect the year for the interview Brenda Spencer gave about the shooting.