The RCMP is leading the probe and says David Riche will fully assess its independence and thoroughness.
Don Dunphy, 59, was shot dead Sunday by an unnamed officer investigating perceived threats against provincial politicians on Twitter.
Riche was appointed to the bench in 1982 and retired as a judge in 1999.
His oversight is "in the interest of transparency and public confidence," RCMP Sgt. Greg Hicks said Wednesday. It's too early to estimate how long the probe will take, he added.
Riche's conclusions will be publicly released with some restrictions to protect privacy and internal procedures, Hicks said.
Premier Paul Davis has said his staff alerted police about the Twitter posts Friday out of concern they could be threats against his family and that of a cabinet minister.
Davis said he was unaware of the online comments until after Dunphy was killed.
Grieving family members asked Wednesday for privacy as they wait for more details from police.
"Our hearts are broken as a result of the tragic and untimely death of our father and brother," said a statement.
The Mounties say the plainclothes officer consulted police databases and local RCMP, who have jurisdiction where Dunphy lived, before heading alone to his house in Mitchells Brook, about 80 kilometres southwest of St. John's.
Hicks has said the officer reported he was invited in, but the mood swiftly changed after about 15 minutes and Dunphy aimed a rifle at him. The investigator responded with "lethal force" using his service pistol, the RCMP said.
The Mounties say a loaded .22-calibre rifle was found beside Dunphy's body and will be examined at a forensics lab. Police have not confirmed if more than one gun was fired.
A spokesman for the Royal Newfoundland Constabulary said its members are not equipped with vehicle or body cameras.
Hicks said an autopsy was done Tuesday but results have not been released.
The killing has raised many questions in the scenic community of about 350 permanent residents on St. Mary's Bay.
Mayor David Sorensen said it's good news that someone besides the police will have a say on the handling of a tragedy many residents believe was avoidable.
"I'm glad that somebody else is going to look at it," he said.
Sorensen said police in the province should be equipped with body and dashboard cameras that can show what happened in cases like this.
Dunphy raised his only child, now a grown woman, alone after his wife died. He was injured in an accident several years ago involving a front-end loader that left him unable to work full-time.
Dunphy spoke out on his battles with the workers compensation system through Twitter, where he described himself as "a crucified injured worker from NL Canada where employers treat (the) injured like criminals."
On Friday, his Twitter feed included posts to the premier's official account and that of Sandy Collins, the provincial minister for child, youth and family services. They referred to God getting politicians who ignored and laughed at the poor before they could enjoy pensions "they didn't deserve."
"I won't mention names this time, 2 prick dead MHAs might have good family members I may hurt."
Sorensen said he's among many people who think the comment was badly misinterpreted as a threat.
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