Crowds of protesters swarmed the streets, facing off with officers in riot gear who fired tear gas and rubber bullets.

Another demonstration in Chicago.

This is a trauma that a lot of us, African-Americans have to deal with.

Please I can't breathe.

A bystander's cell phone video captured the incident Monday night.

A Minneapolis officer pinning George Floyd face down, pressing a knee into his neck.

For at least three minutes on the video, Floyd pleads for help saying "he can't breathe" at least a dozen times.

I can't breathe officer.

Then he becomes unresponsive as onlookers shout at the officer, "Get off of him now."

Security footage from a nearby business obtained by NBC News shows what appears to the moments leading up to Floyd's death.

Officers are seen removing Floyd from a parked car, and handcuffing him before walking him across the street.

In an initial press release, police said they arrived at the scene for a reported "forgery in progress."

And that the suspect appeared to be under the influence and physically resisted officers.

Once the man was handcuffed, police said officers noted he appeared to be suffering medical distress and called for an ambulance.

But the mayor called it wrong on every level.

What we saw was horrible.

Completely and utterly messed up.

This man's life matters.

The 46-year-old Floyd played basketball in college and lived most of his life in Texas, working as a truck driver and security guard.

This is just heartbreaking when you watch how they killed him, how his knee was on his neck, not for one minute, not for two minutes, not for three minutes, not for four minutes but eight minutes.

Lebron James posted this image on his social media, of an officer kneeling on Floyd with former quarterback Colin Kaepernick kneeling in protest of police brutality, writing: "Do you understand now!!??!!?? Or is it still blurred to you??" "

The case is already drawing comparisons to another high-profile police confrontation in 2014.

When you look at that video, what goes through your head?

Oh, I see another senseless killing.

Gwen Carr is the mother of Eric Garner, who died after police in New York placed him in the chokehold.

I can't breathe.

It's like a reoccurring nightmare, and this has to stop.

Something has to be done.