It was the latest in a string of scandals to hit the church in the Netherlands, where an independent commission found last year up to 20,000 minors were sexually abused in Catholic orphanages, boarding schools and seminaries between 1945 and 1981.
In a report released on Thursday, prosecutors said the boys who died between 1952 and 1954 in St Joseph’s psychiatric hospital in the south-eastern town of Heel had likely been given morphine overdoses by Brother Andreas.
Prosecutors said Brother Andreas had died and there were no known living suspects. If he had been alive there was enough proof to launch a criminal investigation.
The Catholic Church has been under fire for years in Europe and North America for sexual offences committed against children over the past century and attempts to cover up the crimes.
In February, a top Vatican official said clergy must report paedophile priests to police.
The Dutch inquiry was launched after the commission found an unusually high number of deaths at the hospital during the period.
It said Guus Vestraelen, the institution’s doctor, had almost certainly covered up for Brother Andreas by misreporting the causes of death. He too has since died.
“On the basis of the facts established… brother Andreas would be a suspect if he were still alive,” prosecutors wrote, noting that any offences committed in the 1950s might have lapsed under Dutch law.
They said the diocese of Roermond, in which the hospital was located, had learned of the deaths by 1958, but had not informed authorities.
“The bishopric finds it inexplicable that it didn’t report these events at the time,” the diocese said on Thursday in a statement on what it called the “disturbing” findings. It expressed regret that an internal investigation carried out in the 1950s had failed to establish the facts.