Rudy Eugene had stripped off the pants of his victim, Ronald Poppo, 65, punched him and then began chewing off parts of his face in an attack that lasted almost 18 minutes Saturday afternoon, footage from security cameras at The Miami Herald showed.
Eugene, who was fatally shot by police when he continued his attack on Poppo after police told him to stop, had been walking naked along MacArthur Causeway when the Herald said he apparently "stumbled upon Poppo by sheer happenstance" in the shade of the elevated tracks of Metromover, a free transit train.
The motivation for the attack remained unclear, the newspaper said.
Poppo, who has lived on Miami's streets for more than 30 years, was in critical condition Tuesday at Jackson Memorial Hospital.
The Herald said Eugene, who was 31, had apparently been in Miami Beach shortly before the attack and his purple 1995 Chevrolet Caprice was towed for being parked illegally.
On Friday night, Eugene had been with his girlfriend in the suburban city of Miami Gardens, and she said he was acting strangely, the newspaper said.
After the attack, some speculated Eugene was under the influence of stimulants or other drugs that can lead to violence, but police said they found no evidence of drugs or paraphernalia at the scene. Toxicology tests of Eugene's blood are likely to take several weeks.