LONDON — A British white supremacist who terrorized the UK by sending hundreds of letters urging people to kill Muslims was sentenced to more than 12 years in prison Tuesday.

David Parnham, a 36-year-old IT systems analyst from Lincoln, admitted to 15 offenses — including soliciting murder, and hoaxes involving noxious substances and bombs — relating to hundreds of letters mailed from June 2016 until his arrest in June last year. Parnham was eventually caught after investigators identified his DNA, handwriting and fingerprints on the letters.

His campaigns included a series of anonymous letters sent to British mosques, and MPs of Muslim descent, threatening them with a fictitious “Punish a Muslim Day” event on April 3, 2018. The letters claimed Europe and North America were being “overrun” by Islam and contained a scorecard for attacks on Muslims, from tearing off women’s hijabs and attacking mosques, to acid attacks and “butchering” Muslims with guns, knives and vehicles.

While the date passed without major violence, the letters caused widespread alarm among Muslim communities in Britain and internationally, as reports of the threatened “event” circulated worldwide. Zara Johnson Elsheikh, chair of the British government’s Counter-Terrorism Advisory Group, told the court that the threats caused “genuine fear and paranoia” across Muslim communities, while hate crime monitoring group Tell MAMA said that Parnham’s letters were referenced in 37 Islamophobic incidents last year.

Parnham also sent a series of letters to mosques and Islamic centers, signed as “Muslim Slayer,” that included drawings of people being beheaded with a swastika-emblazoned sword.

Parnham’s trial revealed that he was apparently radicalized by the crimes of American white supremacist Dylann Roof, who murdered nine African-American parishioners in the Charleston church shooting in June 2015.

In December the following year, Parnham wrote a fan letter to Roof, saying he had become radicalized by the act of terror in Charleston.

“I just wanted to thank you for opening my eyes. Ever since you carried out what I’d call the ‘cleansing’, I’ve felt differently about what you’d call ‘racial awareness’,” Parnham wrote. “My main reason for disgust is Muslims.”

Parnham’s campaign began in June 2016, with letters sent to then-prime minister David Cameron and other public figures that contained a white powder, and were signed off “Allah is great.” A second wave of letters with white powder in October that year were sent to the Queen, Theresa May — who was by that time prime minister — and two bishops.

Judge Anthony Leonard said that Parnham did not appreciate the harm he had caused the Muslim community and society at large, which meant he was at greater risk of reoffending.

“You have yet to appreciate the seriousness of what you have done and seem to want to return to the community at the earliest opportunity to live with your parents,” he said.

He acknowledged Parnham had an autism spectrum disorder, but rejected any suggestion he was psychotic when he committed his crimes. Nevertheless, Parnham will begin his sentence in hospital, until he is deemed healthy enough to be transferred to prison.

Iman Atta, director of hate crime monitoring organization Tell MAMA, told VICE News that the group welcomed Parnham’s sentence.

“David Parnham’s actions were such that it caused extensive fear and trepidation within Muslim communities,” she said. “Many Muslim women called us and asked us whether it was safe to be on the streets on the day of his ‘Punish a Muslim Day’.”

“We are glad that he received a 12 year sentence and that he will have time to seriously reflect on his actions.”