A Lethbridge officer who was captured on video running over a deer with his police vehicle multiple times to kill the animal will not be charged, Alberta's police watchdog has determined.

On Jan. 5, police were called about an injured deer at Scenic Drive and 16th Avenue South.

The officer found a young, female deer, whose hindquarters and rear legs appeared to no longer work and the officer determined the animal was critically injured and needed to be put down.

A video of the incident, captured by a bystander, shows the on-duty officer using a police truck to drive over the animal multiple times for nearly 15 minutes. The animal, which is seen shrieking in the video, struggles to get up several times before eventually dying.

The video sparked protests and tens of thousands signed an online petition calling for the officer to be fired.

"When the officer responded to the call, it was apparent that the animal was suffering and that both policy and common sense required that the officer euthanize the deer to end its continued suffering," Susan Hughson, the executive director of the Alberta Serious Incident Response Team, wrote in an emailed release on Wednesday.

Hughson said the officer determined using his firearm risked the bullet ricocheting and hitting a passing vehicle, nearby home or a bystander. And he didn't have an animal tranquilizer available as it's not standard police equipment.

It is obvious that the decision to kill the deer using the police vehicle was problematic. -Susan Hughson, ASIRT

"The officer's decision to prioritize the very real risk of potential injury to a person over the deer will always be the correct one," she said.

The officer had used his gun in previous situations to euthanize injured deer, evidence showed.

And a firearms expert who reviewed the investigation said he agreed the risk of ricochet was too high, especially given the deer's small size.

Hughson said the officer didn't intend to cause unnecessary suffering, but that the decision to drive over the animal to kill it was an imperfect one.

"With the benefit of hindsight, it is obvious that the decision to kill the deer using the police vehicle was problematic. It did not work as the officer had intended. The deer's ability to move and the inability of the officer to clearly see where the vehicle tires were in relation to the critical organs of the deer frustrated the attempts to cause fatal injury," she said.

But, she said, "no method is or was perfect" and that doesn't mean the officer's conduct was criminal or unreasonable.

The officer told ASIRT that he had reviewed the option of using his baton or knife instead of his gun, but believed driving over the deer would give it the quickest death.

Protesters outside Lethbridge police headquarters in January called for the officer who drove over an injured deer repeatedly to be fired. (Terri Trembath/CBC)

'Impossible to unsee'

But after he drove over the deer the first time, he realized it hadn't done the job.

"He was shocked when he saw the deer was still alive and moving around. It was clear that he had missed the head but felt that the vehicle would have had to have caused crushing injuries to the deer so he felt that death should still be imminent. It was not. Feeling compelled to finish it, and with the firearm still not being a viable option, he continued to use the vehicle until the deer died," Hughson wrote.

He then arranged for city workers to remove the carcass.

"While the events reflected in the video can be clinically recounted, the emotional impact of the video cannot be understated. It was, and remains, profoundly distressing and heartbreaking to watch. It is unforgettable and impossible to unsee," Hughson wrote.

Officer didn't contact Alberta Fish and Wildlife

There was no protocol in place requiring police to contact a vet to deal with injured wildlife. While it could have been done in theory, the practicality of sorting out an out-call to get a vet to a scene late at night "is not quite as easy as it sounds," the investigation found.

The officer also at no point made an attempt to contact Alberta Fish and Wildlife. But he would have known the only officer on call would have likely taken at least an hour to respond as the officer would be coming from Cardston, which is 80 kilometres away, Hughson wrote.

Initially, there had been debate whether ASIRT should investigate the incident or if it should fall under the jurisdiction of the SPCA or Alberta Fish and Wildlife.

Hughson said ASIRT engaged both organizations in the investigation by including a senior fish and wildlife officer on the investigative team and giving the SPCA full access to the investigation.

The SPCA was satisfied that the investigation was fair, she said.

Police chief frustrated by viral nature of story

The video of the officer repeatedly running over the screaming deer was shared widely online and garnered intense and often emotional reactions, something Lethbridge police Chief Rob Davis found frustrating.

At the end of the day, he said the officer's botched attempt to kill the wounded animal pales in comparison to the more serious incidents police deal with on a regular basis.

"On a personal level, I get the emotional attachment [to the deer story]," he said.

"But when you think of some of the other challenges going on in the city (of Lethbridge) and Alberta, some of the violence and the tragic death, if the public would unite and unify when we have a murder or a beating that goes unsolved, that would be a far step for humanity."

"When you see some of the sentences that come out of the judicial system, when you see children being murdered, it gets very little response," he added. "But yet, this was a worldwide story."

Davis said the sudden, intense spotlight was stressful for the the Lethbridge Police Service but it has since died down and they've moved on.

"We're a resilient bunch," he said.

"Obviously there was some stress on the front end but there's so much going on in the city right now, as well. The story ran its course and then we were dealing with other duties."