However, Greaney told members of the jury: "This is no overblown prosecution." What the schoolboy did was "serious and dangerous, and what he intended worse still", he added.
The boy, from Bradford in West Yorkshire, denies making an explosive substance with intent, making an explosive substance and three charges of possession of a document of use for terrorist purposes.
The court heard that concerns about the boy's extremist ideology had begun when he was 13. Over a two-year period culminating in his arrest at 15, his online activity became "progressively dark" as he watched extremist videos and "information about murder and mutilation".
At 14, he spoke to pupils at school about "carrying out a school shooting" and praised Adolf Hitler by stating "gas the Jews". The boy told a police officer he was just showing off, but admitted he had "actually manufactured a drain-cleaning bomb", said Greaney.
The teenager was referred to the Government's Prevent counter-terrorism strategy. He was seen on ten occasions in three months before receiving an official warning in 2017.
But four months later he copied bomb-making instructions on to a CD, detailing how to make a "powerful bomb" that can be used for "killing if shrapnel is added".
Prevent intervened again when he was 15. Greaney said he told fellow pupils "he was going to go on a rampage, aiming to kill many people and then be shot by the police or kill himself". He admitted browsing for guns using a computer with a Nazi SS lightning bolt as the screensaver.
Police then discovered he had been accessing bomb-making information and found CO2 canisters with holes drilled into them. Evidence indicated he had been making a canister bomb. On the same day, he had searched videos about violence against Muslims and pressure cooker bombs.
The case continues.