A BOY accused of planning to carry out a mass atrocity at his school had “viable” recipes for explosives and incendiary devices – including napalm – written into his diary, a court heard.

The jury at Leeds Crown Court heard from expert witnesses during the trial of two teenagers who were arrested last year and charged with conspiring to murder students and teachers at a school in Northallerton.

The boys, who were 14 at the time of arrest and so cannot be named for legal reasons, both deny the charges.

The defendants were found with versions of a bomb-making manual downloaded on to their mobile phones.

The court heard that during the investigation, detectives with the North East Counter Terrorism Unit compared the contents of the manual with the diary belonging to the older boy, which they found included a shopping list of ingredients and instructions for making some of the improvised explosive devices (IEDs) listed in the manual.

One page of the diary included a diagram of “The Ultimate Soldier” which included an outline drawing of a person, with notes pointing to places to carry pipe bombs, smoke bombs and homemade grenades.

The diary also contained a checklist for weapons and items including knives, guns, trench coats and duct tape and also included a key ingredient of a CO2 bomb, which was ticked.

Napalm – which prosecutor Paul Greaney QC reminded the court was used to “terrible effect” by America during the Vietnam War – was also ticked on the boy’s shopping list. He had written out a recipe for napalm into his diary, which detectives from the Counter Terrorism Unit confirmed replicated the manual’s instructions.

A recipe for pipe bombs was also listed in the diary with “add shrapnel for fun” added to the bottom of the text and were included on his shopping list.

Detectives also found a key ingredient found in a recipe for a firebomb ticked in the boy’s checklist, with the words, “some but needs more” written next to it.

Expert witness Vernor Fontanel, a senior forensics scientist and expert in explosive materials and explosive devices estimated the boy’s diary contained a recipe for approximately 1kg of gunpowder.

She said it was enough to cause a “fairly large explosion” and a fire.

The explosives expert also confirmed the boy’s diary contained a viable recipe for napalm, which if used would have created a fireball. She was shown an image for a component of a bomb which the teenager had searched for online and confirmed it could have been used to create an IED.

Prosecutor Paul Greaney told the court how, during his police interview, the teenager said the purpose of his diary was to write down his thoughts to get them out of his system and show his Child and Adolescent Mental Health (CAMHs) worker, as well as impress his girlfriend.

But the court heard that during a multi-agency strategy meeting his mental health worker told police she had not asked the boy to keep a diary and keeping diaries wasn’t part of the working model of therapy.

The trial continues.