VANCOUVER -- The dog that fell from a highrise balcony in Vancouver's Yaletown neighbourhood over the weekend appeared to be trying to get back inside, according to one witness who watched in horror as the disturbing incident unfolded.

The three-year-old Australian shepherd plummeted to its death from the 21st floor of a condo complex near BC Place Stadium on Sunday as bystanders watched helplessly from the street.

The B.C. SPCA said the animal wasn't thrown or pushed, but that investigators are still trying to determine whether cruelty charges are warranted against "the person responsible for allowing the dog to be in that dangerous situation."

Before the animal fell, some onlookers said they could tell the dog was in trouble.

Robert McNeil, who lives in another tower at the same complex, was working out at his building's gym Sunday when he saw a group of people gathering by a window.

He told CTV News he looked up and saw the dog leaning over the railing of a balcony and scratching at the wall, seemingly fixated on a window.

"He was trapped on this balcony and wanted to get back in the building, that's all he was trying to do," McNeil said.

"I kept taking my eyes away from it because it was producing such anxiety in me … it seemed inevitable to me that this dog was going to fall off this railing."

The dog ultimately dropped down onto the patio of a ground-floor unit that was facing the street.

"I don't think there were any children on the street but it was a horrific event to observe," said McNeil, who is also a dog owner. "It was traumatic. You don't shake an experience of witnessing that."

The resident said he saw what he believed to be the same dog barking from the patio about one week prior to the accident.

The SPCA has taken possession of the animal's remains for its investigation, but few details have been confirmed about the circumstances surrounding the fall. It's unclear whether the owner was at home at the time.

McNeil said whatever caused the horrible accident, he hopes it will serve as a reminder to others to keep a close eye on their pets.

"It just seemed 100 per cent preventable," he said.