THE massacre at Columbine High School was the direct inspiration for the teenagers' plot in North Yorkshire.

When prosecutors opened the case against the pair at Leeds Crown Court, the first thing they explained to the jury was what happened in Jefferson County, Colorado, in April 1999.

The court heard how two students at Columbine High - Eric Harris and Dylan Klebold - shot and killed 12 students and a teacher and injured many others.

Prosecutor Paul Greaney QC told the jury: "Eighteen years after the Columbine Massacre and nearly 4,500 miles away, two young teenagers in North Yorkshire became fascinated with Eric Harris and Dylan Klebold.

"The two teenagers researched and discussed those killers and their interest in them turned to hero-worship. It was against that background that they plotted their own attack upon the school they attended."

Columbine was not the first, and was certainly not the last school shooting in the United States.

And it is not even the most deadly.

But "Columbine" has become shorthand for the recurring American horror story of students murdering their own classmates in sometimes inexplicable circumstances.

Since 1999, there have been dozens of other similar atrocities in the United States.

Examples include the Red Lake tragedy - when a 16-year-old went into his former high school on a Native American reservation in Red Lake, Minnesota, with three guns and shot more than a dozen people, killing seven.

Perhaps the most chilling of all American school shooting happened on February 29, 2000 when a six-year-old boy shot classmate Kayla Rolland, also six, at their elementary school in Michigan.

Witnesses are reported to have said the little boy shouted "I don't like you" to his victim.

In December 2012, 20 children and six adults were killed in an attack on Sandy Hook Elementary School, in Connecticut - an atrocity which has rivalled Columbine in its infamy.

But this differs from Harris and Klebold's murders in that the perpetrator was a 20-year-old adult who had left the school many years before.

Part of the shock surrounding the Northallerton plot is that these kind of horrors are seen as a distinctly American phenomenon.

Earlier this year, CNN identified 288 school massacres in the United States since 2009 compared with five in the whole of the other six G7 industrialised countries combined.

The second country on CNN's list was Mexico with eight identified school shooting over the same time period.

Students massacring their classmates and teachers is unheard of in the UK.

The only incident remotely comparable involving an armed attacker in the UK is the Dunblane Masscacre of 1996, when 43-year-old Thomas Hamilton killed 16 children and one teacher in a Stirlingshire primary school.

In 2014, Spanish teacher Ann Maguire was murdered in a Leeds secondary school when her 15-year-old pupil Will Cornick attacked her with a knife.