A security guard threatened a journalist with an imitation pistol during an attempt to sell the latest Harry Potter book, a court has heard.
Aaron Lambert, 20, of Kettering, Northants, admitted trying to blackmail a publisher and threatening a reporter.
In October, he pleaded guilty to stealing two copies of the book from a distribution centre, six weeks before it was due to be released.
The judge remanded Lambert back into custody until sentencing in January.
The bodybuilder was due to face trial after denying that he threatened Sun reporter John Askill with the gun and fired it at him, during negotiations to sell the books.
But in court on Tuesday he admitted all the charges, and two counts of trying to blackmail Potter publisher Bloomsbury. He previously admitted possessing an imitation firearm.
On 2 June, Lambert stole two copies of Harry Potter And The Half-Blood Prince from a distribution centre near Corby where he worked.
He was arrested the following day after two deals with national newspaper reporters went wrong.
While on bail for that, Lambert admits phoning Bloomsbury to extort money from the company.
In court, Judge Richard Bray said: "He (Lambert) is going to prison for a very long time."
Nina Graham, defending, asked Judge Bray for four weeks so a report could be prepared into Lambert's use of steroids in his youth.