A teenage extremist from Derbyshire inspired the suspect accused of killing five people and wounding 17 others in a mass shooting at a gay nightclub in the US, a judge has been told.

Daniel Harris, 19, is facing jail after being convicted of publishing far-right terrorist material from his grandfather’s spare bedroom in Glossop, reported a UK newspaper.

The teenager, who went by the name of BookAnon online, produced videos that called for an armed uprising and celebrated white supremacist murderers including Anders Breivik.

Manchester crown court has previously been told that Harris’s videos were viewed by Payton Gendron, the 19-year-old who killed 10 people in a racially motivated attack in Buffalo, New York, last May.

The judge, Patrick Field KC, was told at a sentencing hearing on Thursday that the material had also been watched by Anderson Lee Aldrich, 22, the suspect accused of a deadly nightclub shooting in Colorado Springs last November.

Harris is facing 12 years in prison and possible extradition to the US after being convicted of five terrorism offences relating to extreme rightwing videos he uploaded to the internet.

He was also found guilty of possessing a 3D printer, which he tried to use to make parts of a firearm. Harris will be sentenced on Friday.

Joe Allman, the prosecutor, told the court that Harris’s connection to the Buffalo mass killer was “well made out” and was “evidence that another has acted on or been assisted by [his videos] in order to endanger life”.

The court was told that Gendron, using his alias Jimboboii, shared and commented on at least two of Harris’s videos, writing to him four weeks before the mass killing: “Thank you for your service.”

Hours after the Buffalo attack, Harris, posting from his grandfather’s house, celebrated the killings in an online video. He was arrested two days later after an undercover sting at a motorway service station.

Further police investigation found that at least one of Harris’s videos, celebrating the gunman who shot dead 51 people in the Christchurch mosque massacre in 2019, had been viewed by Aldrich, who opened fire in a gay nightclub in Colorado Springs on 19 November last year – while Harris’s trial was ongoing.

Allman said the connection to Aldrich showed that “individuals of the greatest concern have accessed the material produced by Mr Harris”. He said the teenager’s videos were “not simply hateful – they’re trying to motivate and instruct”.

The judge, Patrick Field KC, described Harris’s link to the racist Buffalo murders as “wide-ranging”.

Field was told that Harris, who was born in London, is believed to have dropped out of school at the age of seven and was sent to live with his grandfather in Glossop.

By the age of 18 he had convictions for common assault, criminal damage, possession of indecent images of children and racially aggravated damage of a memorial in Manchester to George Floyd, a black man whose murder by a US police officer sparked street protests in the US and UK.

Harris’s barrister, James Walker, said the teenager had acknowledged that “he needs to change his behaviour” but was the subject of “significant failings” by his family and the local authority.

He said the teenager had been exposed to white supremacist material online from the age of 11 and was spending as much as 14 hours a day online.