Moors Murderer Myra Hindley hatched a plan with a prison officer to escape from jail so they could flee together to Brazil, according to Scotland Yard documents.
The previously secret files - seen by the Sun - reveals that the serial killer could have succeeded with the plan in 1973 were it not for an IRA bomb scare.
It has been revealed that Hindley planned to escape from Holloway prison in north London and run away to Brazil to work as a missionary after falling in love with a female prison officer.
The child-killer had even changed her name by deed poll and applied for a driving licence to help with the escape, according to the files released to the National Archive.
Hindley had help from prison officer Patricia Cairns, with whom she had a three-year affair inside the prison.
Cairns used bars of soap to make key impressions for three prison doors as well as the master key for Hindley's D Wing. The soap was smuggled out in a packet of tea to be used to cast key copies.
Cairns planned to meet up with Hindley by the perimeter wall of the prison on a night she was not working. The pair plotted to use a hire car to escape and catch a flight to South America.
In her police statement Cairns confessed: "No definite date had been set for the escape but as for timing I suggested going out at 9pm so Myra and I would have all night to reach our destination before she was missed."
The pair also received help from a second inmate, Maxine Croft - serving three years for forging £5 notes - who agreed to take the soap impressions to a contact to make copies when she was granted a day's parole.
On 29 October, 1973, Cairns planned to drop off a parcel containing the impressions for Croft in the left luggage locker at Paddington station.
Baggage check panic
However, police told the prison officer that the station was not accepting luggage because to an earlier IRA bomb scare. Cairns then made her way to Euston, but panicked when she saw officers checking baggage at the station.
Cairns then posted the package to Croft's contact who agreed to make the keys at a garage in east London.
When the package arrived in Illford, the contact became suspicious of the parcel, fearing it was a bomb. The contact then asked an off-duty police officer to open to package and the plot was foiled.
Cairns was arrested. When officers searched her flat, they found Hindley's false driving licence, in the name of Myra Spencer, as well as latters and photos of Hindley posing in her cell.
Cairns pleaded guilty to plotting the escape plan and was jailed for six years.
Dr Tom Clark, a lecturer at Sheffield University who has studied the records, said the plan was the closest Hindley ever got to going free.
He said: "It was only because of an IRA bomb scare and a suspicious policeman that the plot failed.
"She then turned to more conventional routes to secure her release, but never really came close to having her case heard by the parole board."
Hindley died in in Cookham Wood prison in 2002, aged 60.