An undercover investigation led to nine arrests and the seizure of 77 ATVs and dirt bikes Sunday, after an illegal convoy was intercepted as riders caused havoc on the eastbound Bay Bridge.

Law enforcement authorities warned Monday that they would try to apprehend more of the culprits who brought traffic to a halt with their antics.

“If you made it away yesterday, just expect a knock at your door,” Oakland Police Department interim Chief James Beere said.

The confiscated bikes were worth approximately $200,000 and may be destroyed, Beere said.

Much like sideshows, at which drivers take over intersections to perform doughnuts and other stunts for crowds, mass gatherings of dirt bike and ATV riders have been a nuisance for law enforcement agencies. In March, police seized 85 bikes (opens in new tab) after cyclists tried riding onto the Bay Bridge.

More than 100 officers from the San Francisco Police Department, California Highway Patrol, and other units took part in the two-month investigation, which included undercover cops, according to Oakland Police Capt. Eriberto Perez-Angeles.

On Sunday, officers used drones and an air unit to track the group. Many of those participating in the convoy met first in San Leandro before unloading bikes and ATVs from a flatbed truck at an East Oakland park, police said. 

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The riders’ path took them near Lake Merritt, into Berkeley, and then to San Francisco, where they overwhelmed intersections downtown and in Ingleside for 45 minutes, police said. They encountered police as they returned to the East Bay.

The group was intercepted on the eastbound Bay Bridge. Some riders fled on their bikes; others dismounted and jumped fences. One individual dove into the water before being retrieved by officers and Oakland firefighters and taken into custody.

Throughout, Perez-Angeles coordinated with Oakland’s operations center, SFPD’s Real-Time Investigative Center, and CHP, looking for a safe location to move in without endangering the public or the perpetrators.

Five were arrested for misdemeanors and four for felonies. Two firearms were recovered. All nine arrested Sunday were adults suspected of crimes that include reckless driving, possession of firearms, and outstanding warrants. Two others had been arrested Friday on suspicion of organizing and promoting a sideshow.

Beere acknowledged that the arrest count was modest given the operation’s scale, citing pursuit policies and the chaos of the scene. “We’re not going to risk the participants’ safety, officer safety, or general public safety,” he said. “We had plenty of evidence to follow up on.”

There were no injuries resulting from the arrests, officials say; some individuals were reportedly injured as they fled.

License plate readers, surveillance cameras, and an expanding drone fleet enabled officers with the SFPD and OPD to track the group, often without the riders knowing they were being watched, according to SFPD spokesman Evan Sernoffsky.

“That wouldn’t have been possible before both of our agencies had the technology we have today,” Sernoffsky said.

With San Francisco lacking a police helicopter unit for roughly 20 years, drones have become essential for aerial surveillance, he added.

Sernoffsky said the SFPD’s sideshow response unit has seized 140 vehicles over the past year, most through follow-up investigations. “These cases are far from over when they occur,” he noted, suggesting that additional arrests may follow Sunday’s operation.

After breaking up the ride, investigators returned to the East Oakland staging area and towed vehicles that had allegedly transported bikes and ATVs, Beere said.

“We will go up and down the state of California with warrants for your bikes or your illegal vehicles,” he said. “This is not over.”