The training and resources of the Lethbridge police officer seen repeatedly running over an injured deer on a city street are being called into question by a wildlife expert, who says a person should “never, ever” euthanize an animal by running it over.

Nigel Caulkett, a professor of veterinary anesthesiology at the University of Calgary, has over 30 years of experience researching the safe capture and handling of animals as well as the euthanasia of animals. He has focused much of his research on pain and pain management in deer.

Caulkett said situations in which officials are called to dispatch an injured animal can be very stressful, but responding officers should be trained in humane ways to euthanize an animal in distress.

WATCH: A longtime wildlife expert is weighing in on the troubling video that shows a police officer running over an injured deer in Lethbridge.

2:08 Backlash mounts after Lethbridge police officer repeatedly runs over deer Backlash mounts after Lethbridge police officer repeatedly runs over deer

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In the video, filmed by a Lethbridge resident on Saturday night, the officer can be seen running over the young, injured deer several times as the animal is heard shrieking.

“In my experience working with deer in painful situations, it’s incredibly rare that they vocalize, that they cry out, and that deer did that a number of times so I actually found it very difficult to watch,” Caulkett said, adding he was horrified when he first watched the video.

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He said he’s been in similar situations throughout his career and that proper training and resources are key when it comes to dispatching an injured animal.

“I sympathize with the officer somewhat because you do need the right tools to do your job,” Caulkett said. “I know there’s been some talk about (how) he should have used his service firearm. I’m not sure what they have in Lethbridge — if it’s a nine-milimetre or a .40 Smith and Wesson — but either of them at close range would do the job, but the bullets they use don’t necessarily stay in the animal, and I think there would have been a worry about human safety if the bullet exited or if the hit wasn’t appropriate and ricocheted the bullet.”

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Caulkett said he’s been working with other wildlife management agencies to study a frangible bullet — which would enter the animal’s head and then break into fragments, instead of leaving the animal’s body — that could be used for animal euthanization, but officers would still need the proper training and resources to use that method.

WATCH: Calgary veterinary professor says firearm may not have been best option for Lethbridge police officer

1:00 Calgary veterinary professor says firearm may not have been best option for Lethbridge police officer Calgary veterinary professor says firearm may not have been best option for Lethbridge police officer

Another system that’s often used is what Caulkett described as a penetrating captive bullet, which would never leave the gun from which it’s fired.

In rare situations where an animal is really suffering and a responding officer doesn’t have proper resources, Caulkett said wildlife officials also recommend what’s called a “quick kill,” which involves a quick cut to the animal’s carotid and jugular arteries. He added that if he were in the officer’s shoes, he would have contemplated using that method.

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Death threats made against officer

The Alberta Serious Incident Response Team (ASIRT) said Wednesday that it’s launched an investigation into the officer’s actions in killing the deer. ASIRT said death threats have been made against the unidentified officer involved.

“While the video publicly released is evidence, which must now be properly secured, it reportedly captures only a portion of the incident,” ASIRT said in a release. “A full, fair and objective investigation must include additional investigative steps to ensure admissible evidence as to what occurred prior to the commencement of the video, the circumstances surrounding the taking of the video and chain of custody, the identification and interview of available witnesses, relevant communications and training and securing any other evidence that may be relevant to the event.”

READ MORE: Deer season: What to do if you see wildlife on the road

ASIRT said it’s working with Alberta Fish and Wildlife and the Alberta SPCA through the investigation, which will look at police officers’ powers in dealing with the dispatching of animals in relation to the provisions outlined in the Criminal Code, the Animal Protection Act and the Wildlife Act.

WATCH: Calgary veterinary professor explains difficult situation Lethbridge police officer faced with injured deer

1:37 Calgary veterinary professor explains difficult situation Lethbridge police officer faced with injured deer Calgary veterinary professor explains difficult situation Lethbridge police officer faced with injured deer

ASIRT called the video “disturbing” and said it has prompted calls to several agencies including the SPCA, ASIRT, Lethbridge police and Fish and Wildlife officials.

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“Call centres for all the above agencies have been overwhelmed by the volume of calls and complaints that they are receiving,” ASIRT said. “This has resulted in a disproportionate strain on both the resources of these agencies and their staff, who very much care about the treatment of animals.”

What’s the proper response?

Caulkett said it’s his understanding that when responding to an incident involving injured wildlife, any officer is required to call Fish and Wildlife or another peace officer to get permission to euthanize the animal.

“There can be a lag phase, but the times I’ve had to do it… I’ve been able to obtain permission very quickly,” he said.

When asked on Tuesday about whether Fish and Wildlife was contacted, Lethbridge police Chief Robert Davis said that to the best of his knowledge, wildlife officials had not been called. He also could not confirm whether the responding officer called to ask for permission or guidance before killing the deer.

He said running over an animal until it is dead is not part of the training Lethbridge officers receive and that ASIRT will be investigating the protocols the police force has in place as well as the officer’s actions.

Davis said the typical protocol would be for the officer to determine whether the animal was injured so severely that it needed to be euthanized, then take into account public safety when looking at how to kill it.

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“Our policy speaks to euthanization of animals typically through a firearm, but again, you bring in a firearm you really ramp up the need for public safety,” he said.

“My whole career, you deal with an animal by shooting it. However, there may be circumstances where that’s not practical and if that’s a gap that’s identified in the investigation then we’ll rectify that gap. At this time I’m not familiar with any processes outside of [use of firearm].”

WATCH: University of Calgary professor Nigel Caulkett walks us through a humane animal euthanization

1:11 Calgary veterinary professor demonstrates humane animal euthanization Calgary veterinary professor demonstrates humane animal euthanization

In an emailed statement from Lethbridge police on Wednesday, the service said it’s dealing with a “large backlog of voicemails, emails and social media messages regarding the video of an officer and an injured deer.”

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“While we appreciate the many concerns that have been expressed to us, regrettably we do not have the capacity to respond directly to every individual call and message,” LPS said.

“We are asking the public to exercise patience to allow the independent investigation by ASIRT to progress without interference.”

The statement went on to say that because the investigation is now in the hands of ASIRT, neither LPS nor the Lethbridge Police Commission can comment further.

The Calgary Police Service told Global News it determines the best approach for dealing with animals in distress on a case-by-case basis.

“Generally, officers are trained to attempt to locate an injured animal’s owner or to contact Animal Control or Fish and Wildlife officers where practical,” CPS spokesperson Corwin Odland said in an emailed statement.

“If officers believe an animal is unduly suffering and they cannot relieve the suffering while waiting for assistance, the animal can be humanely euthanized using a firearm, if it is safe to do so.”

Global News’ requests for comment from Fish and Wildlife on the incident and proper procedures were not returned by the time of publication.

As the investigation continues, ASIRT is asking any members of the public that either directly witnessed the incident or recorded any portion of it to contact them at 403-598-4306.

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The officer involved in the incident will remain on active duty throughout the investigation, Lethbridge police said Tuesday.

A protest is scheduled to take place at the Lethbridge Police Service headquarters from 2 p.m. to 5 p.m. on Sunday. Organizers demanding the officer involved be fired and charged with animal cruelty.