It would make a "mockery" of the justice system if Toronto police officer James Forcillo is given the mandatory minimum sentence, the officer's lawyers argue in a constitutional challenge to sections of the Criminal Code.

Constable Forcillo, who was convicted of attempted murder in the shooting death of Sammy Yatim during a confrontation on a Toronto streetcar, is asking a judge to strike down the mandatory minimum provisions that would send him to prison for four years (or five if his gun is deemed to be a restricted weapon). He is also challenging a section that prohibits a conditional sentence in the case.

"This is not about giving state actors special treatment," the officer's lead lawyer, Peter Brauti, said in written submissions filed in Ontario Superior Court earlier this month. "It is about ensuring that when we ask men or women to arm themselves to protect the larger community, we will treat them justly and fairly when they make mistakes concerning how they use force because we placed upon them the responsibility of engaging in the conflict in the first place."

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The officer's acquittal on a charge of second-degree murder means the use of lethal force was justified and the mandatory minimum penalty is "grossly disproportionate" to the conduct that resulted in his attempted murder conviction, his lawyers argue.

Superior Court Justice Edward Then will hear the constitutional challenge beginning on May 16 as part of the sentencing process for Constable Forcillo, who is free on bail. The Crown is expected to file its written submissions early next month. A jury acquitted Constable Forcillo, 32, in January on the charge of second-degree murder in the death of Mr. Yatim, but convicted him on the lesser charge of attempted murder.

The officer fired two volleys of shots at Mr. Yatim, who was armed with a small switchblade, shortly after midnight on July 27, 2013. A pathologist determined that one of the first three shots was the cause of death. A second volley of six shots, as the 18-year-old student lay mortally wounded on the floor of the streetcar, was the basis of the attempted-murder charge.

The constable's lawyers refer to the facts of the case as unprecedented in their written submissions and say no other Canadian officer has been convicted of attempted murder in the line of duty.

The Supreme Court of Canada just last week struck down a mandatory minimum penalty of a year in prison for potentially low-level drug trafficking.

Michael Dineen, a Toronto defence lawyer who was part of a successful challenge at the Supreme Court to the mandatory minimum sentences for illegal gun possession, says the timing may be good for the officer. "After the overuse of minimum sentences by the government of Stephen Harper, there is a new appetite for protecting judicial discretion on sentencing," he said.

The conviction of an officer on a charge of attempted murder is highly unusual, Mr. Dineen agreed. However, relying on the fact the defendant is a police officer may not necessarily be beneficial. "That cuts both ways. Officers also have huge responsibilities as well, in the use of a firearm," he said.

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The mandatory minimums for attempted murder with a firearm are not new. They were introduced by the Liberal government of Jean Chrétien in 1996 and changed slightly by the Conservatives in 2008.

A minimum may be found to be unconstitutional if it is overly broad and requires punishment that is excessive based on the circumstances. Constable Forcillo's lawyers use the hypothetical example of a battered woman who lawfully shoots her abusive partner, but then fires again after mistakenly believing he is about to get up, and is charged with attempted murder.

Four years in prison for Constable Forcillo (or five, depending on how the court interprets the section that relates to the handgun he was required to carry), "is a sentence that not only fails to reflect the principles and purposes of sentencing in the Criminal Code, it would make a mockery of those principles and purposes," Mr. Brauti states.