Police arrested one of the suspects on an unrelated charge last month and then hit the jackpot when they searched his cellphone. They found video files showing the dogfight. And the faces, police say, of those involved.
The video shows two pit bulls fighting as their owners and bystanders provoke them to fight harder.
"They're kinda slapped and punched and yelled at and set back at each other and they fought pretty viciously for about five minutes until the video cuts off," San Francisco Police Inspector Dan Silver said. Silver is with the gang task force.
Police believe the dogfight happened in March at the Hunters View housing development.
They arrested three men who police say are documented members of the Westmob gang.
"Westmob does robberies, murders; there've been rapes, burglaries, drug dealing," Silver said.
Police say Ed Perkins owns one of the dogs. They say Acie Lee Mathews Jr. is the owner of the other pit bull. Jermaine Jackson was apparently a bystander at the dogfight. Being a spectator at a dogfight is also a crime.
When police searched Jackson's home, they found a pit bull mom and her three puppies and a bulletproof vest and ammunition.
Silver also recognized 19-year-old Jaquan Rice from the video. He was shot to death three months after the dogfight at a bus stop in the Bayview. Rice was himself the victim of an almost fatal mauling by two pit bulls when he was only eleven years old.
Police also found other videos of pit bulls on Perkins' cellphone. One showed two of them apparently being trained to bite by attacking hanging tires.
Silver suspects pit bull street fighting goes on more than we know.
"It's not all uncommon practice at all," he said. "It is a vastly underreported practice, I believe.
Silver told ABC7 News that street gangs use dogfighting as a means of controlling their turf.
"It just creates just increasing air of violence and intimidation in the neighborhood," he said.
Police believe one of the dogs may have died but they would like the public's help finding them. And if anyone recognized any of the other people in the video, they would also like to know who they are.