Larry Vega told WSVN-TV in Miami that he was riding his bicycle Saturday afternoon off the MacArthur Causeway that connects downtown Miami with Miami Beach when he saw the savage attack on the bridge's off-ramp.
"The guy was, like, tearing him to pieces with his mouth, so I told him, 'Get off!'" Vega said. "The guy just kept eating the other guy away, like, ripping his skin."
The slain man was identified by the Miami-Dade County Medical Examiner's office as Rudy Eugene, 31, Miami television station WFOR reported.
Vega flagged down a Miami police officer, who he said repeatedly ordered the attacker to get off the victim. The attacker just picked his head up and growled at the officer, Vega said.
As the attack continued, Vega said the officer shot the attacker, who continued chewing the victim's face. The officer fired again, killing the attacker.
Miami police have released few details about the attack, other than confirming that there was a fatal officer-involved shooting. The name of the victim, who was taken to Jackson Memorial Hospital, had not been immediately determined by authorities, said Detective William Moreno. Messages left Monday for a police spokesman were not immediately returned.
A spokeswoman said Monday that the hospital would not be releasing any information about him.
A surveillance video camera from The Miami Herald building nearby captured images of the men's naked legs lying side by side after the shooting.
Vega said the victim appeared gravely injured.
"It was just a blob of blood," Vega said. "You couldn't really see, it was just blood all over the place."