Ashraf Islam, 31 -- formerly Mark Townley -- had gone to Thailand last spring to prepare for the operation before returning to London in May to carry out the plan, prosecutors said Friday at Islam's sentencing hearing.
Islam said the prince "had blood on his hands" after two tours of duty in Afghanistan, The Daily Telegraph reported Friday.
Islam told authorities he worked on physical fitness and conducted online research for 10 days in Thailand before flying to London, but then became "scared and nervous" and turned himself in to police May 23 and confessed, the report said.
Islam pleaded guilty two days later to one count of making a threat to kill.
Prosecutor Lynne Townley said at the sentencing hearing Islam told police he had planned to pose as a tourist at a military color guard event and disarm a soldier so he wouldn't have to risk carrying a weapon into the country.
Notes on Islam's computer indicated he planned to dress like a "biker" so as not to be taken for an "Islamist extremist."
A video on his computer showed Islam expressing plans to kill Harry, the newspaper said.