Ivo Poppe, a 61-year old Catholic deacon in Belgium, went on trial this week under the suspicion of killing at least ten people, including multiple family members.

In 2014, Poppe was arrested after telling his psychiatrist that he had “euthanized” dozens of people, according to the BBC.

Based on the deacon’s diary, the death toll could exceed reach as high as 50.

Most of the alleged victims died from an injection of air into their bloodstream, causing fatal embolism. Among those who died were multiple relatives, including Poppe’s 89-year old mother, his two great-uncles, and his father-in-law. Poppe had claimed that his mother wanted to be euthanized, but her doctors denied that she had expressed any wishes to end her life.

Before he became a deacon, Poppe was a nurse and worked for 20 years at a clinic in the town of Menin.

Poppe, made two partial confessions during an investigation, saying that he killed “out of compassion, to spare the physical and mental suffering” of his victims, according to Expatica.

However, Poppe later withdrew his confessions and now denies  the murder charges against him.

Cardinal Jozef De Kesel, head of the Poppe’s diocese during the killings, offered the church’s full cooperation in the investigation, saying he was “stunned” by the accusations, Expatica reported.

Officials from the diocese will testify at Poppe’s trial, along with other witnesses, relatives, and psychiatrists.

The trial, which started on Monday in the northwest city of Bruges, is expected to last two weeks. If convicted, Poppe would be considered the most prolific serial killer in Belgian history.