A retired priest has been charged with indecent assault following a decade-long investigation into a residential school in Manitoba, Canadian police said on Friday.

Arthur Masse, 92, was arrested and charged on Thursday with a single charge of indecent assault on a 10-year-old girl at Fort Alexander Residential School in Manitoba.

The assault by Masse took place between 1968 and 1970 while the girl was a student and the allegations were brought forward in February 2010. A criminal investigation was launched in 2011.

"The size and scope of this investigation has meant many years of investigative work," said Sgt. Paul Manaigre, Media Relations Officer with the Royal Canadian Mounted Police (RCMP) in Manitoba.

The school was built on the territory of the Sagkeeng First Nation and closed in 1970. Reuters was unable to immediately reach the priest or his lawyer for comment.

Canada's residential school system operated between 1831 and 1996 to assimilate indigenous children. They were run by several Christian denominations on behalf of the government, most by the Catholic Church.

A report released in 2015 by the Truth and Reconciliation Commission of Canada documented the atrocities, including rape and malnutrition, suffered by many of the children who attended the schools.

RCMP Officers said they obtained 75 witness and victim statements, but due to the passage of time, many couldn’t participate. 

"The emotional trauma experienced by victims of abuse is very real, and despite the years that intervened between the alleged occurrences and when police were investigating, that trauma is still present,” Manaigre said.

This is the only investigation into residential schools underway by the Manitoba RCMP, it said.

Pope Francis will visit Canada at the end of July and is expected to apologize for the Catholic Church's role in running the schools.

Masse was released with conditions that he will appear in court on 20th July.