“Tell the police of Bergamo that the killer of Yara Gambirasio was here. May God forgive me,” the handwritten note said, according to a report in Corriere della Sera.
The book, from the Salvini di Rho chapel hospital, has now been passed to forensic experts, along with CCTV footage, the newspaper said.
Chapel staff told La Stampa that they did not notice anyone in particular, suggesting that the note was left a few hours before it was discovered.
“The book is normally full of the thoughts of the faithful, with thanks to the doctors,” a member of staff said.
Enrico Pelillo, the Gambirasio family’s lawyer, said they still had hope the killer would be found.
“Whether the letter was written by a compulsive liar or not, it is important that we do not stop investigating. We have a duty to give answers to a family that has waited for months, in silence, to know the truth,” he told La Stampa.
The teenager went missing on November 26th 2010 after leaving a gym in Brembate, a village between Bergamo and Milan.
Despite the efforts of search teams, Gambirasio’s decomposed body was not found until February 2011, in a clearing in Chignola d’Isola, 10km away from Brembate, Corriere said.
The autopsy revealed that the girl had suffered a head injury and had been stabbed in the back, neck and wrists. She was left for dead by her attacker and subsequently died from the cold, La Stampa said.
Gambirasio was clothed when found and was allegedly murdered for trying to stop a planned sex attack, Corriere said.
Investigators have amassed 14,000 DNA samples but have been unable to find her killer.
The evidence first pointed to Mohamed Fikri, a builder in the Bergamo region, but this hypothesis was later dismissed by police, La Stampa said.
In March 2013 investigators exhumed the body of truck driver Giuseppe Guerinoni, who died a decade ago, based on DNA evidence found on the girl’s clothing.
As Guerinoni died long before the murder happened, investigators believe that the killer could be his son from an illegitimate relationship in the 1960s or 1970s, Italian media reported. The truck driver’s son has not yet been found.