A sentencing hearing for the highest ranking officer involved in the massive civil liberties breach that stained the chaotic G20 summit six years ago is set to begin Wednesday.

The two-day proceeding for Toronto police Supt. David (Mark) Fenton is expected to hear widely different views on what his sentence should be for discreditable conduct and ordering unlawful arrests.

The prosecution wants him demoted for a year. The officer says a reprimand would be enough or, at most, the loss of five vacation days. Complainants who were "kettled" — some for hours in a torrential downpour — want him fired.

Fenton was convicted last August under the Police Services Act of two counts of unlawful arrest and one of discreditable conduct for his actions during the weekend summit in June 2010. The charges related to two incidents of "kettling" in which police in full riot gear trapped scores of people at downtown intersections.

In finding him guilty, the retired judge presiding over the hearing, John Hamilton, said Fenton demonstrated a lack of understanding of the right to protest when he ordered detentions and mass arrests that weekend.

The extreme measures to which the officer resorted, even though he was handed a difficult situation, were unnecessary and unreasonable, Hamilton concluded.

Following the guilty finding — which came after years of delays in the proceedings — the officer apologized through his lawyer, saying he regretted the indiscriminate arrests and detentions in the pouring rain that left people soaked and shivering.

More than 1,000 detained during G20 weekend

The G20 weekend, marred by a spate of vandalism in which store windows were smashed and two cruisers set alight, saw one of the largest mass detentions in Canadian history. About 1,100 people — most of them peaceful protesters or innocent bystanders — were detained or arrested, many ending up in a widely condemned makeshift detention centre.

Fenton, a 27-year member of the Toronto police force, was found not guilty of charges related to the cage-like temporary jail.

He is the only upper command officer to face disciplinary proceedings for his summit actions. Another senior officer, Supt. Gary Meissner, was similarly charged but opted to retire before his hearing, putting him beyond the reach of the Police Services Act.

Their boss, then-chief Bill Blair, was not required to testify at Fenton's hearing — and has since become a member of Parliament in the Trudeau government.

Earlier this month, Ontario's highest court ruled two lawsuits against police arising out of the G20 could proceed as class actions.