ACAPULCO, Mexico (Reuters) - Mexican prosecutors charged three police officers on Monday with burning a taxi driver to death in the trunk of his car in a case that set off a day of street protests by taxi drivers. "For the moment they are being charged with homicide," Acapulco prosecutor Salvador Calleja told reporters. Authorities said four additional police officers were being investigated in the death of Jesus Gallegos. When Calleja left his office on Monday, he was swarmed by about 100 angry taxi drivers, resulting in a scuffle between the protesters and city officials. Gallegos had a minor traffic accident with a police patrol car on Sunday night, leading to an argument during which police began beating him in front of bystanders, officials said. "They had no mercy with him," his widow, Maria Ojilve Mondragon, told reporters. "He was working, and they took him out of the car, beat him up and took him (outside town) to dump his body." Other taxi drivers found his burned-out taxi on Monday morning on an unpaved road on the outskirts of Acapulco.