A Roman Catholic deacon and former nurse went on trial in Belgium on Monday suspected of killing at least 10 people, including his own mother, by injecting air into their veins.

Ivo Poppe, 61, dubbed the “Deacon of death” by local media, would be one of the worst serial killers in Belgian history if convicted in the trial in the town of Bruges.

Poppe was originally arrested in 2014 after authorities were told that he had confessed to his psychiatrist that he had “actively euthanised dozens of people.”

He made two partial confessions during the inquiry, but later retracted them and has since denied the charges against him.

Poppe spent 20 years working as a nurse at a clinic in Menin, near the French border, and another 10 as a pastoral visitor after being ordained as a deacon.

He is formally accused of killing at least 10 people including his mother, three other relatives and two patients.

But officials believe the real toll could be much higher, with the inquiry having established a list of at least 50 suspect deaths based on notes in his diary, which included a count of fatalities at the clinic.

Most of the suspected victims died from an injection of air into their bloodstream.

He claimed during the investigation to have acted “out of compassion, to spare the physical and mental suffering” of people often nearing the end of their lives.

The final victim he is accused of killing is his own mother, who died in 2011 aged 89, while she was suffering from depression.

Her doctors however denied that she wanted to be euthanised as her son had claimed, Belgian media reported.

The trial is set to last two weeks and include testimony from dozens of witnesses, relatives, psychiatrists and officials from the diocese.

Cardinal Jozef De Kesel, the head of the diocese at the time of the killings and now the most senior Church figure in Belgium, said in 2014 that he was “stunned” by the allegations and pledged the full cooperation of the Roman Catholic authorities.

The trial in Belgium began as a male nurse serving a life term in neighbouring Germany for killing six hospital patients with lethal drugs out of “boredom” will face trial for another 97 murders.