A cellphone video of a Lethbridge, Alta., police officer repeatedly running over an injured deer has emotions running high, with calls for criminal charges, reports of death threats against the officer and a flood of complaints to government agencies.

In the video, published by Global News, an on-duty officer is seen using a police truck to drive over the deer multiple times in south Lethbridge, trying to kill it for nearly 15 minutes. The animal eventually died.

"I watch a lot of animal cruelty videos, unfortunately for my job, and this is among the worst that I've ever seen," said Camille Labchuk, an animal rights lawyer with Animal Justice, noting it's a criminal offence to cause an animal unnecessary pain or suffering.

"It's very apparent from the video that the deer was experiencing horrific pain and suffering. You can hear the deer shrieking and screaming and crying out."

The Alberta Serious Incident Response Team (ASIRT), which normally reviews police officers' use of force on other humans, is taking the exceptional step of investigating the case. It's the watchdog's first file involving an animal. Alberta SPCA and Alberta Fish and Wildlife are assisting with the investigation.

In another rare move, ASIRT issued a lengthy statement Wednesday afternoon about the open investigation.

"It is recognized that this is an extremely sensitive and serious matter where there has been considerable public interest," the agency said.

"ASIRT will examine a police officer's powers relating to dealing with events such as this and will consider the relevant provisions within the Criminal Code, the Animal Protection Act and Wildlife Act."

It certainly does not meet the criteria for a humane death. - Darrell Dalton, registrar of the Alberta Veterinary Medical Association

The watchdog said the cellphone video, which triggered its investigation, is disturbing but captures only part of the incident.

It's promising a full investigation that considers what happened before the recording, the circumstances surrounding the recording and what any other witnesses may have seen, among other evidence.

Darrell Dalton, registrar of the Alberta Veterinary Medical Association, said he can't comment on whether this is a case of animal cruelty, without knowing the circumstances surrounding why the officer used his truck the way he did.

"It certainly does not meet the criteria for a humane death," Dalton said. "It's not rapid, it's not painless and does not reduce distress and suffering."

Dalton said when officers find an injured animal they normally use their firearms, not their vehicles.

This passion… must not supersede reason. - Alberta Serious Incident Response Team

"I think some police officers are reluctant to do it, but I know of police officers that have dispatched animals at the side of the road with their sidearm."

When asked why the officer did not use his gun, a Lethbridge police spokesperson said they cannot comment on the case while it's under investigation.

ASIRT said concerned citizens have overwhelmed the phone lines of various agencies, including Fish and Wildlife, Alberta SPCA and Lethbridge police, resulting in a "disproportionate strain on both the resources of these agencies and their staff, who very much care about the treatment of animals."

"This passion, however, must not supersede reason," the agency said.

"The situation has escalated to reported death threats against the unidentified officer."

If you see injured animal, call authorities

ASIRT is asking the public to remain patient and to "exercise restraint so that the investigation can proceed without interference and so that these and other agencies can move forward and continue their important work."

Labchuk, the executive director of Animal Justice, said anyone who finds an injured animal at the side of the road should call authorities, such as wildlife officials who can make the call about "whether and how to dispatch the animal."

Alberta Fish and Wildlife can be contacted at 403-310-0000, or here is a list of the department's regional offices.

Thousands have signed a petition for the officer who drove over the deer to be fired, and a protest is planned for outside police headquarters on Sunday.