Brian Lawrence, who was convicted of killing a friend of his ex-lover and hiring a hitman to kill two others, hoped to use the Isle of Wight Festival as cover once free from Parkhurst prison on the island.
The 67-year-old communicated with his accomplices using lemon juice as invisible ink and codes hidden in sudoku puzzles. In the letters he drew maps and gave encrypted instructions for his plan to bring a helicopter into a part of the prison grounds not protected by nets. He intended to fund the escape plan using the sale of a quarry in Newbury, Berkshire, worth £500,000 (€600,000).
But the plot, which had the aim of reaching Spain, was uncovered when prison guards spotted the phrase “more heat, less light” in one of his letters.
They then found the invisible messages which can be seen when the paper is heated up from underneath.
Lawrence, who is serving a life term, was then transferred to another prison.
Barry Greenberry, governor of HMP Isle of Wight, which is an amalgamation of Parkhurst, Albany and Camp Hill prisons, said: “I am delighted at the way our security team and Hampshire Constabulary have foiled a possible escape attempt... I am very proud of the operations team at HMP Isle of Wight who diligently pieced together intelligence to stop a security breach.
“This is exactly the sort of excellent public service that the police and prison service provide to protect the public and reduce re-offending.”
Lawrence, a retired schoolteacher, was found guilty at Reading Crown Court of battering a friend of his ex-lover, Korean War veteran Deryk Cox, 69, to death before setting fire to his house in Caversham, Berkshire, in 2003. He then set out to hire a hitman to kill two other people.
Lawrence, from Hermitage, Berkshire, was caught after an undercover policeman posed as a hitman. The trial heard that Lawrence had become “insanely jealous” of other men close to his married ex-lover after their three-year affair ended.