ROME — An Italian nun who was stabbed 19 times more than two decades ago by three teenage girls apparently fascinated by Satan was honored Sunday with beatification as a martyr of the Catholic Church.

Hours before the beatification ceremony in northern Italy, Pope Francis praised Sister Maria Laura Mainetti and described her killers as “prisoners of evil.” Beatification is the last formal step in the Catholic Church before possible sainthood.

Italian news reports about the June 6, 2000 slaying in the town of Chiavenna said the defendants during interrogation recounted that the nun asked God to forgive her attackers even as they assaulted her.

After serving sentences ranging from 8 1/2 to 12 years and four months, the convicted attackers were released from prison. Two were age 16 and the other was 17 when the Catholic nun was slain. They were prosecuted as minors.

Addressing the faithful in St. Peter’s Square during his traditional Sunday remarks, Francis spoke of the beatification, saying Mainetti, who belonged to the religious congregation of the Daughters of the Cross, was slain “by three girls influenced by a satanic sect. Cruelty.”

According to other Catholic clergy in the town, Mainetti went out of her convent late at night after receiving a call from one of the girls who said she became pregnant after being raped and needed help. Prosecutors later described that as an invented story to lure the nun from the convent. The nun was struck repeatedly by a brick or a stone, then stabbed 19 times in an unlit alley.

Francis said Mainetti “loved young people more than anything else, and she loved and forgave these same girls, prisoners of evil.”

The pope said the nun’s legacy was her “life program — do every little thing with faith, love and enthusiasm.”

The alley where the 60-year-old nun was slain is now a pilgrimage site. Brought to the Chiavenna sports stadium for the beatification ceremony was a bloodstained stone found where she was slain.

Scribblings about the devil were reportedly found in the teens’ writings, prompting prosecutors to hypothesize that fascination about Satan was the apparent motive for the killing. But later, news reports said one of the teenagers reportedly told investigators they killed the nun to “do something different.”