A British man who fantasized about assassinating Prince Charles with a rifle and compared himself to Norwegian mass killer Anders Behring Breivik has been detained indefinitely under mental health laws.

Mark Colborne was convicted of planning terrorism in September. Prosecutors said the 37-year-old wrote about his hatred for “non-Aryans” and about how he was “looking for major retribution, a mass terrorist attack.” They said he suffered from depression and felt marginalized as a white, red-haired man.

Colborne was arrested in June 2014 after his family uncovered chemicals, items related to making lethal poison and notes detailing his racial hatred in his bedroom.

Judge John Bevan said Tuesday that Colborne was a “warped individual” whose “extraordinarily violent fantasies” were seriously concerning.