Around 22:00 on 6 June 2000, Mainetti left her convent in Chiavenna and went to a local public square to meet a girl who had recently requested an appointment via telephone, claiming to have been raped and impregnated and to be considering an abortion. There, Mainetti encountered the girl, Veronica Pietrobelli, and the latter's friends, Milena De Giambattista and Ambra Gianasso. The three girls, aged 16 and 17, lured Mainetti down a nearby street to a secluded area outside a park where they ambushed her, stoning and shouting abuse at her before taking turns in stabbing her with a kitchen knife that De Giambattista was carrying. Mainetti prayed as she was being attacked, asking God to forgive the girls, before dying after having been stabbed 19 times. Mainetti's body was found the next morning by a passerby. The girls were arrested on suspicion of the murder three weeks later, after two of them discussed what they had done in a telephone conversation—police had monitored the girls' telephones after a witness claimed to have seen them with Mainetti. In custody, the girls initially said they killed the sister "for sport", later saying they killed her in a
satanic sacrifice. They told investigators they had initially wanted to kill the parish priest, but decided that Mainetti, who had previously taught them
catechism, would be an easier target; After a
summary trial at the juvenile court of Milan on 9 August 2001, De Giambattista and Pietrobelli were convicted of murder and sentenced to 8 years and 6 months' imprisonment, with the court taking into account that they were partially
insane at the time of the crime; their sentences were later upheld by the city's appeal court. Gianasso, who was initially found not guilty of murder by reason of insanity, was sentenced to 12 years and 4 months' imprisonment by the appeal court on 4 April 2002; she was released on 17 January 2003 after the
Supreme Court of Cassation failed to reach a verdict on an appeal she had filed, before returning to prison six days later after the court upheld her sentence. By 2008, all three perpetrators had been released from prison after participating in
community service programs. == Legacy and beatification ==