Video footage posted to social media Tuesday morning shows a Minneapolis police officer kneeling on the back of a handcuffed black man's neck as he struggles to breathe and onlookers repeatedly warn the cop he is crushing the man to death.

The Minneapolis Police Department said in a statement Monday night that the man—who was identified Tuesday as George Floyd—died of an unspecified "medical incident" shortly after being transported to a local hospital, but eye-witnesses described the incident as outright murder.

"It is sickening to watch this black man be killed while helplessly begging for help. Black lives matter isn't just a chant, it's call for justice. It's a call for our humanity to be recognized. This must stop."
—Rep. Ilhan Omar

"The police killed him, bro, right in front of everybody," said Darnella Frazier, who filmed the incident and posted a 10-minute clip on Facebook. "He was crying, telling them like, 'I can't breathe,' and everything. They did not care... They killed this man."

Floyd repeatedly says in the video that he cannot breathe as an officer keeps one knee on the back of his neck, forcing the victim to remain sprawled out face-first on the asphalt. The Minneapolis Police Department said the officers were responding to a "forgery in progress" and claimed Floyd "physically resisted officers."

"He's talking, he's fine," one of the officers on the scene says as bystanders plead in the video with the other cop to take his knee off Floyd's neck.

"You're fucking stopping his breathing there, bro," replies one witness. Floyd eventually lost consciousness, but the officer continued kneeling on his neck until an ambulance arrived minutes later.

Watch [warning, the footage is graphic and may be disturbing to witness]:

National civil rights attorney Benjamin Crump said in a statement Tuesday that he has been retained to represent the Floyd family.

"We all watched the horrific death of George Floyd on video as witnesses begged the police officer to take him into the police car and get off his neck," said Crump. "This abusive, excessive, and inhumane use of force cost the life of a man who was being detained by police for questioning about a non-violent charge. We will seek justice for the family of George Floyd, as we demand answers from the Minnesota Police Department. How many 'while black' deaths will it take until the racial profiling and undervaluing of black lives by police finally ends?"

Minnesota authorities and the FBI are investigating the incident as the video continues to spread on social media, sparking widespread outcry and demands for justice.

"My heart is breaking for the tragic loss of life last night near 38th and Chicago," Minneapolis City Councilwoman Andrea Jenkins, who represents the neighborhood where the incident took place, said in a statement. "Our community continues to be traumatized again, and again, and again. We must demand answers."

Rep. Ilhan Omar (D-Minn.) tweeted that "it is sickening to watch this black man be killed while helplessly begging for help."

"Black lives matter isn't just a chant, it's call for justice," said Omar. "It's a call for our humanity to be recognized. This must stop."