The F.B.I. and Minnesota law enforcement authorities are investigating the arrest of a black man who died after being handcuffed and pinned to the ground by an officer’s knee, in an episode that was recorded on video by a bystander and that sparked large protests in Minneapolis on Tuesday.
After the graphic video circulated widely on social media, the mayor denounced the actions of the four officers who were involved and said on Tuesday afternoon that they had been fired. He identified the victim as George Floyd.
Mr. Floyd, 46, a resident of St. Louis Park, Minn., a Minneapolis suburb, was pronounced dead at 9:25 p.m. Monday at Hennepin County Medical Center, according to the medical examiner.
Mr. Floyd’s family members told CNN on Tuesday night that the officers should be charged with murder.
“They treated him worse than they treat animals,” said Philonise Floyd, Mr. Floyd’s brother. “They took a life — they deserve life.”
The arrest took place on Monday evening, the Minneapolis Police Department said in a statement, after officers responded to a call about a man suspected of forgery. The police said the man was found sitting on top of a blue car and “appeared to be under the influence.”
“He was ordered to step from his car,” the department’s statement said. “After he got out, he physically resisted officers. Officers were able to get the suspect into handcuffs and noted he appeared to be suffering medical distress.”
The statement said that officers had called for an ambulance.
On Tuesday morning, without referring to the video recorded by a bystander, the police updated a statement, titled “Man Dies After Medical Incident During Police Interaction,” that said that additional information had “been made available” and that the F.B.I. was joining the investigation.
On Tuesday afternoon, Mayor Jacob Frey of Minneapolis tweeted that four officers involved in the case had been terminated. “This is the right call,” he said.
The Police Department’s statement said that no weapons had been used and that the officers’ body cameras were recording. Mr. Frey said at a news conference Tuesday that he had seen the video “taken and posted by a civilian” but not the body camera footage.
The bystander video shows a white Minneapolis police officer pressing his knee into a black man’s neck during an arrest, as the man repeatedly says, “I can’t breathe,” and, “Please, I can’t breathe.”
As the video spread on social media on Monday night, the arrest quickly drew comparisons to the case of Eric Garner, a black man who died in New York police custody in 2014 after an officer held him in a chokehold. Mr. Garner’s repeated plea of “I can’t breathe” — also recorded by a cellphone — became a rallying cry at demonstrations against police misconduct around the country.
“Being black in America should not be a death sentence,” Mr. Frey said in a statement on Tuesday. “For five minutes, we watched a white officer press his knee into a black man’s neck. Five minutes.”
Former Vice President Joseph R. Biden Jr., the presumptive Democratic presidential nominee, condemned the force used by the officers.