The man convicted of manslaughter in the 2007 death of York Regional Police officer Robert Plunkett is applying to have his 12-year sentence reduced.

A 22-year veteran of the force, Plunkett died while investigating a stolen air bag ring in August 2007.

Plunkett was working undercover when he tried to arrest Nadeem Jiwa on a residential street in Markham, Ont. Jiwa tried to resist arrest and as he fled, his reversing car pinned Plunkett against a tree, causing injuries that later proved fatal.

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Robert Plunkett died on duty in August 2007. (York Region Police) (York Regional Police)

If his appeal is successful Jiwa, who has served five years of his sentence, could be set free.

Plunkett's widow Sonja Plunkett was at the courthouse Wednesday and said the appeal is difficult for her family to digest.

"This has been a very long journey and this is a chapter we weren't expecting," she said.

Jiwa's lawyer Clayton Ruby, however, said Jiwa's 12-year sentence is too harsh and should be cut in half.

"Other courts have found in similar circumstances that six years is a really powerful deterrent," he told CBC News. "How many years do you have to give someone before they get the idea or the public gets the idea that killing officers is wrong?"

Jiwa's lawyers will also argue their client didn't know Plunkett was a police officer because he was in plain clothes.

John Miskiw of the York Regional Police Association said Jiwa should serve out the remaining years of his sentence.

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Nadeem Jiwa, 23, was convicted of manslaughter in April for his role in the death of York Region police Det.-Cst. Robert Plunkett. ((Alex Tavshunsky/CBC))

He called the request for a six-year sentence "totally inappropriate."

"Mr. Jiwa knew that he was dealing with a police officer," he said.