A man who shocked people at a Calgary grocery store by unleashing a racist tirade against a young brown-skinned grocery store cashier and customer has contacted police, after another customer captured video of part of his rant and a physical attack.

The last 37 seconds of the incident at the Sunridge Real Canadian Superstore in Calgary's northeast on Saturday was captured on video by another customer, Steven Lemmon, who shared it with media.

The angry customer seen in the video contacted the Calgary Police Service late Monday and agreed to meet with investigators at a later date.

"Me and my girlfriend and my youngest child were just trying to buy groceries," Lemmon told CBC News on Monday.

"On the way to the checkout we heard the start of the altercation. I was standing about five feet away from the whole entire thing."

Lemmon says the incident seems to have started with an item that was accidentally scanned twice.

Witness Steven Lemmon says he hopes a racist attack on a cashier and customer, can lead to something positive. (Julie Debeljak/CBC)

He says the cashier — who looked to be between 16 and 20 — immediately called his manager to fix the problem.

"Before the manager even got there, [the customer] began with just immediate racial attacks on the cashier. When the manager got there, it didn't stop. He continued the racial attack on the cashier. He threatened to rip his chain off and jam it down his throat. He called him out to the parking lot. This is a kid," Lemmon said.

Then another customer, also brown-skinned, stepped up and told the irate customer to calm down, he said.

That's when Lemmon started recording a video, when the angry customer could be heard calling the second customer a "bomb-making motherf--ker."

This man unleashed a racist tirade on a grocery store cashier, then a customer who stood up to him. Part of the incident, which happened Saturday at the Sunridge Real Canadian Superstore, was caught on video. (Screengrabs from video submitted by Steven Lemmon)

"He immediately turned his attention to that guy. 'Mind your f---ing business,' as you see on the video, he two-hand shoved the gentleman and then continued with a racial tirade on him. I have never seen anything like that, honestly.

"I took [the video] because it was getting so racially motivated and I knew it was going to turn physical. I knew the guy was angry enough that something was going to happen."

Lemmon said the angry man then left the store.

'Feel so entitled doing it'

"It was like he was untouchable. He gave everybody the middle finger. He left there on top of the world and it shocked me to see that somebody could do something like that and feel so entitled doing it."

Calgary police took questions from reporters Monday about this and other racial incidents over the weekend.

Staff Sgt. Paul Wyatt said members of the Calgary Police Service's diversity unit visited the store "to speak to store staff and provide any support that we can to them with regards to education and training and dealing with those types of incidents."

Staff Sgt. Paul Wyatt says they want to speak with the victim to learn to context of the video. (CBC)

The customer who was shoved in the video has not spoken to police.

"Obviously, we'd like him to come forward to Calgary police and tell his side of the story," Wyatt said.

He said an assault charge is possible but police "need to know the full story" before such a charge could be laid.

"It would be too early for me to say charges are forthcoming," he said.

"We do have that 30-second snippet on video. Obviously, some of the language is offensive and some of the gestures, and what happens looks quite violent, but we don't know what precipitated it."

He added that the Crown determines whether an incident can be treated as a hate crime or not.

'Deserves somebody to stand up for him'

Meanwhile, Lemmon says despite his disgust with what happened, he's still optimistic it could be a learning moment.

"I sincerely hope that something good comes of it," Lemmon said.

"Canadians are an apologetic people. We all like to think that there was an underlying issue that that man was going through that day. I would just like to see him apologize to that young man and the other young man and the people of minority groups in the store that day."

Lemmon said when he posted the video to Twitter, he began to get threats directed at him, but they were mostly from anonymous troll accounts.

"I'd like to think that my children are going to grow up in a world where those events don't happen inside of a grocery store," he said.

And Lemmon has a message for the young cashier.

"He deserves somebody to stand up for him. He deserves to know that he is welcome to work in that store and he doesn't deserve to take that on any given day."