Extended surveillance video of a brutal beating of a car chase suspect by two Alameda County sheriff’s deputies in San Francisco corroborates witness reports that a third deputy had taken a valuable gold necklace from the beating victim, San Francisco Public Defender Jeff Adachi said Wednesday.

But an attorney for the deputy who had been put on leave following the theft allegations said she did not think the footage showed anything definitive.

Adachi said the slowed-down and enhanced version of the video he posted on his office’s YouTube channel confirms a homeless couple’s account that a deputy gave them cash and jewelry taken from 29-year-old Stanislav Petrov as a way to bribe them to not discuss the beating they saw.

Petrov was beaten in an alley in San Francisco’s Mission District on Nov. 12 by Alameda County sheriff’s deputies Luis Santamaria and Paul Wieber. Alameda County sheriff’s officials said Petrov had led deputies on a 38-minute chase from Castro Valley after ramming two patrol cruisers in a rental car whose lease had expired.

Surveillance camera footage shows the deputies knocking Petrov to the ground, punching him and clubbing him with their batons, even after he appeared to surrender with his hands on his head. According to Petrov’s attorney, he suffered broken bones in his hands from the beating, as well as head wounds and a concussion.

More of that same footage, Adachi said, catches a third deputy, identified as Shawn Osborne, in the act of taking Petrov’s gold chain.

“This is a point in time in the video, about 10 minutes after the beating,” Adachi said. “It appears a deputy is twirling what looks like a metallic necklace, consistent with the necklace that was taken from Petrov and given to the homeless couple. It looks like he picked it up from where the beating occurred, and he starts walking to the area where the homeless couple says it was given to them.”

Gabrielle Lurie/Special to The Chronicle

Alison Berry Wilkinson, who is representing Osborne, said the poor quality of the video made it difficult to comment. The footage, though blurred and grainy, shows the deputy with something in his right hand.

Wilkinson had previously called the theft and bribery allegations “absolutely outrageous.” She said Osborne had gotten lost while following the chase and did not arrive until the ambulance arrived.

The video of the deputy at the scene was just “a snippet, which is misleading,” as well as “incredibly difficult to decipher,” Wilkinson said.

“What (Adachi) posted there certainly doesn’t show enough to draw the conclusion that he’s claiming,” she said.

All three of the deputies are currently on paid leave, said Sheriff’s Office spokesman Sgt. J.D. Nelson. He said the agency was aware of the extended video.

“We’ve known about it a while, and this is part of our investigation,” he said. “We’ve already taken the steps to remove that deputy from work. This certainly was part of that, and it will certainly be part of what I believe to be a pending criminal matter in this incident.”

Prosecutors with the San Francisco district attorney’s office are investigating whether to file criminal charges against the deputies involved. Nelson said the FBI had been asked by the district attorney’s office to enhance the video. Max Szabo, a spokesman for the district attorney, declined to comment because of the ongoing investigation.

Adachi expressed dismay that the district attorney’s office has not made a charging decision, six months after the beating.

“Eyewitnesses have come forward with detailed accounts that corroborate what’s seen on the footage,” he said. “Isn’t that enough for the San Francisco district attorney to bring criminal charges against these deputies?”

Attorneys for Petrov filed a claim last month against the Alameda County Sheriff’s Office. Petrov is currently in federal custody on gun and drug charges.

Vivian Ho is a San Francisco Chronicle staff writer. Email: vho@sfchronicle.com Twitter: @VivianHo