Refusing to provide a breath sample after a fatal crash is just as grave a crime as impaired driving causing death, the Supreme Court of Canada has ruled.

But the high court also found that the sentence handed down could be more lenient if the accused person followed bad legal advice - or if they fell victim to vigilante justice.

Friday's 6-1 ruling stems from an incident in May 2013, when Richard Suter hit the gas pedal instead of the brakes of his SUV, plowing in to an Edmonton restaurant patio and killing two-year-old boy Geo Mounsef.

Writing for the majority, Justice Michael Moldaver upheld a 2008 law that makes refusing to provide police with a breath sample when death is involved just as serious and punishable an offence as impaired driving causing death.

But he noted that Suter's case was unique.

"The fact that Mr. Suter was not impaired at the time of the accident; that he refused to provide the police with a breath sample because of ill-informed and incorrect legal advice; and that he was attacked by vigilantes and had his thumb cut off with pruning shears, are all factors that must be taken into account in creating an appropriate sentence," the judgment reads.

Following the advice of his lawyer, Suter had refused to blow into a breathalyzer after the crash. The trial judge ruled the incident a non-impaired accident and handed him a four-month sentence, citing bad legal advice and the fact he was a victim of vigilante justice as mitigating factors.

An Appeals Court later upped that sentence to 26 months in prison.

Vigilante justice shouldn't be given too much weight

The Supreme Court found a more appropriate sentence would be 15 to 18 months, which means Suter's sentence is set aside and replaced with one of time served. Suter already served more than 10 months in jail.

The ruling said if there had not been extenuating circumstances, a sentence of three to five years would have been appropriate, given that refusing to blow in a breathalyzer after a fatal crash is "an extremely serious offence."

"Parliament has made this clear. It carries with it a maximum punishment of life imprisonment, and with good cause, the judgment reads. "When a person refuses to provide a breath sample in response to a lawful request, this deprives the police, the court, the public at large and the family of the deceased of the best evidence as to the driver's blood alcohol level and state of impairment."

Mitigating factors

The ruling found that vigilante justice can't be used to reduce a sentence to the point it becomes disproportionate to the gravity of the offence, but it can be a mitigating factor.

"Violent actions against an offender for his or her role in the commission of an offence necessarily form part of the personal circumstances of that offender, and should therefore be taken into account when determining an appropriate sentence," it reads.

"However, vigilante violence should only be considered to a limited extent, as giving it too much weight at sentencing allows these kinds of criminal conduct to gain undue legitimacy in the judicial process."

The judgment said that other courts have found acts of violence against an inmate that were triggered by the offence the person is in custody for have also been considered as a factor in sentencing.

"Although being assaulted by a fellow inmate is not the same thing as being abducted and attacked by vigilantes, the rationale for taking these collateral consequences into account when sentencing an offender remains," it reads.

Suter's lawyer, Dino Bottos, said his client felt "somewhat vindicated" by the ruling.

"He described it as having gone through five years of hell," he said. "But he also wanted to say to the Mounsef family that he is deeply sorry for what he has done and the death of Geo Mounsef caused by him and that he's going to live with that for the rest of his life.

"His punishment will never be over and he knows that," Bottos said, adding that Suter suffers from PTSD.

