About 100 animal rights advocates protested outside Lethbridge, Alta., police headquarters Sunday, calling for an officer who repeatedly drove over an injured deer to be fired and charged with animal cruelty.

A video obtained by Global News shows an 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.

"I think hearing that deer scream will haunt me for quite a while," said protester Keith Gregory. "This should not be allowed to happen in our society and the fact that [the officer is] still on the job is disgraceful."

Police have not released the name of the officer, who remains on active duty while the investigation takes place.

Protesters, some of whom were accompanied by their pet dogs, carried signs reading "say no to animal cruelty" and "all life is precious," with photos of deer.

Micki Gerstenbuhler said this was her first time protesting, adding that she can't comprehend how the officer kept driving over the animal repeatedly as it was suffering.

"He needs to be held responsible … once that deer started to cry, how could you continue the torture? It's so unfathomable to me," she said.

Heather Anderson, founder of Calgary animal rights group The Daisy Foundation, said some protesters travelled from as far as Edmonton and Saskatchewan to have their voices heard.

She said she's dealt with a lot of animal rights cases, but this one will stick with her.

"This was horrible. Honestly, I will have nightmares for a long time," she said.

'We have to be animals' voices'

The Alberta Serious Incident Response Team (ASIRT), the police watchdog that reviews officers' use of force on people, is investigating the case — its first file involving an animal.

The agency said it will consider relevant provisions within the Criminal Code, Animal Protection Act and Wildlife Act.

According to ASIRT's website, the agency has been involved in 389 investigations from 2008 to mid-2018, resulting in charges against 32 officers.

Protesters stand outside Lethbridge police headquarters Sunday, criticizing an officer who drove over an injured deer multiple times to kill the animal. (Terri Trembath/CBC)

Lethbridge police have said they will not provide any further details while ASIRT's investigation takes place.

Gregory said he doesn't have faith ASIRT will end up charging the officer, saying the agency hasn't charged officers who have shot and killed humans.

"I don't think anything's going to happen," he said.

Joelle Withers, another first-time protester, said she wants there to be more compassion when dealing with animals.

"The third or fourth time he ran her over, she was still lifting her head up … she doesn't have a voice, so we have to be animals' voices."

As of Sunday afternoon, more than 65,000 people had signed an online petition calling for the officer to be fired.