A SINGLE text message may be the only thing that stopped Sienna Johnson from becoming America’s next mass shooter, prosecutors say.

On the same day US President Barack Obama shed tears over the country’s endless cycle of gun violence, the 16-year-old schoolgirl fronted a court accused of a planning an atrocity that has left her community cold.

Sienna was arrested in December and charged this week with plotting to kill her classmates and teachers at Mountain Vista High School in Colorado in the days before Christmas. According to police, she had “taken overt and substantial steps” in her deadly plan.

As the world learns the details of her alleged plot, the identity of a fellow classmate and alleged accomplice has yet to be released.

Chillingly, the school where the two girls allegedly planned to carry out the attack is just 16 kilometres down the road from Columbine High School — the site of America’s most notorious school shooting. And that’s no coincidence.

In the lead up to the planned massacre, prosecutors say Sienna had made a number of online references to the film Natural Born Killers, reports the Denver Post.

The movie became an obsession for Columbine shooters Dylan Klebold and Eric Harris, who made frequently cited the film in the vast materials they left behind following their 1999 massacre.

Sienna also allegedly made references to a number of other school shootings on her Tumblr page, which was dotted with violent images. Prosecutors will claim that the girl had done her homework on the school shooters she wanted to emulate.

According to NBC 9 News, Sienna had made detailed maps of the school grounds, with markings of where different groups of students hung out. She had also obtained a schedule of police officers assigned to the school.

In the later months of 2015, she purchased a BB gun for shooting practice, according to reports. However, a lawyer for Sienna’s co-accused has told a juvenile court there was no direct evidence the other girl was in possession of “any weapons, bombs or incendiary devices.”

‘MAYBE IF YOU’D MADE ME PRETTY’

In her smiling selfies, Sienna Johnson doesn’t look like someone contemplating — or capable — of carrying out a massacre. She did however reportedly show signs of troubling and even dangerous behaviour.

During court proceedings this week, the prosecution called the teenager “extremely violent” and claimed she had harmed her pets in the past.

In the wake of her arrest, she was being treated at a psychiatric facility at a local children’s hospital and allegedly admitted to police that she was “faking her mental progress”.

Sienna’s lawyer, Ara Ohanian, told reporters Colorado police and prosecutors had “grossly exaggerated” the case against his young client.

The local District Attorney strongly disagrees.

“This has the potential to be something that is of extreme significance to members of this community,” George Brauchler said, adding the evidence — much of it sealed — bear out exactly what the pair had in store.

Sienna’s Webly page is filled with images of written notes and what look like stream of consciousness writings. The scribblings appear to be authored by her and give a dark insight into a seemingly troubled mind.

“I feel very stranded and alone. I still think people like me best when I only show what they want to see and I’m not so nervous anymore so maybe I can be easier to love. And now the air is clear and the sky is blue,” she wrote. “I still feel very alone and very isolated and very betrayed.”

In the “About” section of the page, she details her family life and how it became more difficult when her dad remarried. At the bottom of the page she includes a number of happy childhood photos.

She wrote of how she found solace in punk rock music, writing and art.

“I still put all my time and energy into the things I enjoy most and hope to be the best I can be.”

In typical teen scrawl in a journal, she writes of being “so rotten, so moody, so unhappy”.

“Dear god, maybe if you’d made me pretty inside and out I’d be like sugar and spice and all things nice.

“I’ve been so unclean.”

THE RISE OF COLUMBINE COPYCATS

In a powerful article published by the New Yorker in October, Malcolm Gladwell detailed how the cult of school shooters has manifested itself in a new generation of disenfranchised and angry youth.

“School shootings are a modern phenomenon,” he noted.

Gladwell referenced sociologist Ralph Larkin, who made the case that by leaving behind a website, extensive documents, videos and a lengthy manifesto, the Columbine shooters laid down the “cultural script” for the next generation of mass killers.

Larkin examined 12 major school shootings in the United States in the eight years following Columbine, and found in eight of them the shooters made explicit reference to Harris and Klebold.

Among the common traits displayed by those keen to join their ranks is a focus on the ritual of the attack. The focus is on the emerging “traditions” associated with school shootings, rather than the deadly consequences.

In the wake of her arrest, Sienna allegedly told police if she was released, she would try to carry out the massacre again, but would be more discreet about her plans.

Prosecution says Johnson has showed no remorse, told detectives if she got out she'd try again. — Jennifer Kovaleski (@JennKovaleski) January 5, 2016

Her alleged co-conspirator is reportedly undergoing psychiatric testing under police guard.

Meanwhile a judge has ruled that Sienna will be prosecuted as an adult. The 16-year-old is being held in jail awaiting trial on a $US1 million bond.

“We still feel she is a danger to the community,” Deputy District Attorney Deborah Wrenholt told the court.

Sienna is charged with two felony charges of conspiracy to commit first-degree murder.

Police say an SMS tip off to the force’s ‘Text-A-Tip’ service days before Christmas led to the discovery of the alleged plot.