Two correctional officers are facing criminal charges after a lengthy investigation into the death of Matthew Hines, a 33-year-old federal inmate who asphyxiated after enduring repeated blasts of pepper spray from staff.

On Wednesday, the New Brunswick RCMP announced charges of manslaughter and criminal negligence causing death against two men, 48-year-old Alvida Ross and 31-year-old Mathieu Bourgoin. Both officers have been on administrative leave and will appear in Moncton Provincial Court on Feb. 26.

The Union of Canadian Correctional Officers issued a statement saying it is "supporting these officers to ensure they have adequate representation, as they are presumed innocent until proven guilty."

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Mr. Hines died at Dorchester Penitentiary, a Correctional Service Canada (CSC) facility 42 kilometres southeast of Moncton, on May 26, 2015. Officials initially ruled it a natural death. But after 2 1/2 years, at least four investigations and a determined effort by Mr. Hines's family, outside investigators reviewing the case have ruled the death a criminal act.

"We are relieved that the cause of Matthew's death in prison has been thoroughly investigated," the family said in a statement to the media. "Our parents waited far too long to be told the truth of how Matthew died, and now we feel that it is fundamentally important to all Canadians that justice be done, and be seen to be done."

CSC said it has co-operated fully with the investigation and is committed to "learn from Mr. Hines's death and continually work to improve our response to individuals in medical crisis," spokeswoman Laura Cummings said in an e-mailed statement.

The family's current understanding of the death contrasts starkly with the official story they heard in the days and weeks immediately after the tragedy.

Upon Mr. Hines's death, CSC issued a news release saying he had been discovered by staff "in need of medical attention." Investigators with the New Brunswick RCMP quickly ruled out foul play. The family was told he died of a seizure.

By 2016, the case seemed closed. But in May of that year, authorities asked the Mounties in neighbouring Nova Scotia to review the case after new information came to light.

Around the same time, the Hines family received a copy of an internal CSC investigation. It revealed that Mr. Hines had been pepper-sprayed five times on the night of his death, challenging the official explanation of natural causes.

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The family shared the report with the media, drawing high-level scrutiny to the file.

"I cannot comment on the specifics of this incident while authorities continue to examine it, but let me be clear that there can be no tolerance for inappropriate use of force or other serious misconduct," Public Safety Minister Ralph Goodale said that August. "Correctional staff have difficult jobs, but any allegation of inappropriate behaviour must be thoroughly and transparently investigated, and the appropriate consequences must follow."

CSC now concedes there were problems with its initial explanation. "We acknowledge there was inaccurate information in the initial news release about Mr. Hines's death," Ms. Cummings said. "That was due to staff errors, and for that we have apologized."

In May last year, the independent Correctional Investigator, Ivan Zinger, released a report detailing his own investigation. He found numerous "staff errors and omissions" contributing to Mr. Hines's demise and criticized all levels of CSC, from correctional officers on the scene to senior staff who released misleading information and skirted accountability.

"Nearly everything that could have gone wrong in a use of force response went wrong," Dr. Zinger's report states.

It also narrates a chilling series of events. At 10:11 that night, Mr. Hines, who was serving a five-year sentence for bank robbery and other crimes, was headed to his cell for the night when he turned around and started talking with a correctional officer.

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Two additional officers soon appeared on the scene to wrestle Mr. Hines, a heavy-set man with a history of mental illness, to the floor. They struck his torso and head with their knees and fists, opening a bloody wound on the left side of his face.

The tussle stopped – only to flare up again three minutes later. Mr. Hines fell to the floor once again, face down, hands cuffed behind his back.

Even though five correctional officers appeared to have the inmate under control, one officer pepper-sprayed Mr. Hines, the report says.

As several officers "frogmarched" him backward to the segregation unit, an officer shot two bursts of pepper spray "seemingly without warning or reason, directly in Matthew's face."

The officers then moved him to a shower stall, where he pleaded for help, made a series spitting or choking sounds and lapsed into convulsions.

The officers dragged him from the stall by his feet. His lack of movement didn't seem to bother an inexperienced duty nurse who appeared on the scene but did not check his vital signs.

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By 10:31 p.m., someone had called 911 for an ambulance. A doctor at the Moncton Hospital declared him dead shortly after midnight.

A pathologist ruled that "the cause of death appears to be acute asphyxia due to extensive pulmonary edema following administration of pepper spray."

In their statement, the Hines family complimented the Nova Scotia RCMP and suggested that responsibility for the death reaches well beyond the two accused.

"Although we have been told and accept that only two correctional officers are facing criminal charges under the Criminal Code of Canada," the statement reads, "we trust that all who saw Matthew before and during his death look in the mirror every day with the knowledge of what they did and did not do."