SAN FRANCISCO (KGO) -- One Bay Area police department is being accused of not searching hard enough for evidence. You've heard of caught on tape, how about cleared by tape? In one example shown to ABC7 News, a man was thrown in jail for stealing a cellphone, but surveillance video shows he wasn't even there at the time. And we're learning he may not be the only one.Attorneys at the San Francisco Public Defender's Office says they are seeing a disturbing number of cases against innocent people who are eventually exonerated by video evidence.There have been at least three cases in San Francisco since July where suspects have been arrested and charged with felony crimes, only to have their charges dropped, or a jury acquits them, because they were not the ones who committed the crimes. The Public Defender's Office blames police for failing to investigate those crimes thoroughly.On July 28, police arrested Dahmu Dameron shown on video hanging out in the Tenderloin and charged him with snatching a cellphone from a pedestrian -- a felony robbery. Three witnesses told police Dameron was the culprit. He was jailed for two weeks before public defender investigators found security video that exonerated him. One store camera recorded Dameron hanging on a corner near the robbery.A block away, another camera showed several men walking toward the victim on the right of the screen. One grabs his phone. Both cameras had the same time stamp. In other words, Dameron couldn't be in two places at the same time.San Francisco Deputy Public Defender Andrea Lindsay explains, "Mr. Dameron is standing there, minding his own business, having no involvement whatsoever in the cellphone snatch."In August, police arrested Rafael Blazquez-Covarubias, shown in a video taken near the corner of Capp and 15th streets, and charged him with attacking a man with a razor scooter and robbing him. Officers said they found security video from a nearby school."They reviewed video at the school and they write in their report that in fact there's nothing on this video," Lindsay says.But public defenders investigators reviewed the same video and this is what they found: Blazquez-Covarubias is at a bench with a woman when two men approach him. He backs off as if to defend himself. The men walk after Blazquez-Covarubias. In a video, you see him walking backwards as his attackers walk toward him.He is clearly not the aggressor. But he was arrested and spent about a month in jail before his charges were also dropped.Lindsay says they're seeing more cases where police are not seriously looking for videos to make their cases. She explains, "It's resulting in a lot of innocent people sitting in custody, charged with serious crimes.""All I can say is we've got one of the best video retrieval units in the nation," says San Francisco public information officer Carlos Manfredi.Manfredi points to the videos officers retrieved from the fatal Pier 14 shooting this summer of Kate Steinle that led quickly to the arrest of the suspect. And he also cites the security videos that led to the arrest in February of the man who police say chopped up a body in dragged it in suitcase downtown."To say they're able to get the video that's terrific, but to say we're not doing enough, that's just ludicrous," says Manfredi.The public defender believes the same effort to look for videos is not always made in lower profile cases. They also point out that the arrests are on your record unless you expunge them or go to court and get a motion approved for factual innocence.for full coverage on the Pier 14 shooting