Two RCMP officers justifiably shot and killed a sexual-assault suspect who went on a drug-fuelled rampage in a front-end loader near Red Deer on Christmas Day 2015, an investigation has found.

"The force used was necessary and reasonable in all the circumstances, notwithstanding the tragic outcome," Susan Hughson, executive director of the Alberta Serious Incident Response Team, told a news conference Monday in Edmonton.

"Operating this front-end loader in the manner he did resulted it becoming a weaponized, 35,000-lb. blunt instrument that was much more difficult to stop or contain than any other standard vehicle."

Early on Dec. 25, 2015, a man who had been taking methamphetamine visited the residence he shared with his common-law partner, ASIRT's investigation found. It's alleged the man sexually assaulted his partner and committed other violent acts against the person.

He fled the scene. After a series of 911 calls, Red Deer RCMP learned the 37-year-old might be driving a stolen truck.

When an officer located the stolen truck near Sylvan Lake and tried to pull it over, the man reversed at high speed into the police vehicle, disabling it and causing minor injuries to the officer. The man drove off.

He then stopped at a rural home of people he knew, requesting money, a cellphone and keys. When the residents refused to help, the man drove the stolen truck into the home and into a snowmobile in the yard, then drove away.

The truck was found abandoned in a Caterpillar Finning lot in the Edgar Industrial Park in Red Deer. The man had climbed into a CAT 937K front-end loader and was driving it through the area.

Loader driven onto Highway 2

He drove through a fence into a parking lot and struck multiple vehicles, ramming them or flipping them over.

He was next located in a nearby field, driving the loader into and over stacked hay bales.

With RCMP in pursuit, he drove briefly onto Highway 2, "where he came within feet of civilian vehicles on the roadway," Hughson said.

RCMP called for more assistance, including from a helicopter.

front-end loader crime spree

These police photos were taken in the aftermath of a shooting near Red Deer, where a man in a stolen front-end loader smashed into several vehicles. (Supplied)

At 1:30 p.m., two officers in separate unmarked vehicles tried to set up spike belts on Range Road 273A. The man saw them and drove directly at the officers.

One officer, in a Dodge Charger, backed into a driveway and the front-end loader followed. The man used the machine to pin the officer's car against a tree, then tried to bring down its bucket onto the roof with the officer inside.

The second officer, who was then on foot, began firing his service pistol into the cab of the front-end loader. The other officer got out of the Charger and also fired on the man.

Suspect died at the scene

The front-end loader went into a nearby field and moved around in a large circle in the field. Officers saw the operator slumped over on the floor of the cab, not moving. He was pronounced dead at the scene.

Hughson said officers may use lethal force when they believe someone presents a risk of death or grievous bodily harm to another person.

Susan Hughson

ASIRT executive director Susan Hughson told reporters the officers took the necessary actions to protect themselves against an aggressive man.

"In this case, the situation had gone beyond the mere perception of risk," she said.

"The man's actions, in ramming the police vehicle while the officer was still inside, pushing it into a tree, and trying to lower the bucket down onto the roof of the vehicle, placed that officer at imminent risk of grievous bodily harm or death. And only the split-second decision to use lethal force prevented that from happening."