Over the past week, brazen groups of thieves — some tallying as many as 90, riding in caravans with dozens of vehicles, wielding hammers and sometimes guns — have ransacked high-end stores across the Bay Area before racing off with tens or hundreds of thousands of dollars in merchandise.

The crimes, some caught on video, have drawn national attention and prompted action from local law enforcement and Gov. Gavin Newsom, who are promising to do a better job protecting retailers. The question police and criminologists are asking now is whether this crime cluster is the sign of a troubling new trend and, if so, what’s driving it and how big an impact it might have on local and national crime rates.

David Ball, a Santa Clara University law professor, said the pandemic lockdown, social and civil unrest, and widespread economic displacement have created conditions that need to be studied carefully to answer those questions.

“All of those are really extraordinary changes,” Ball said. “We need to be sure that the data we are seeing is signal and not noise. Is this actually a new trend?”

With the holiday shopping season well underway, this news organization asked police, crime experts and retailers to put these crimes in context and explain where the stolen goods go and what can be done to prevent more such thefts.

Is retail theft on the rise in California?

San Francisco and Los Angeles have historically been among the top 10 cities reporting the most loss from theft nationwide, said Rachel Michelin, president of the California Retailers Association. That makes it difficult to track if these specific thefts are causing spikes in crime numbers.

Comprehensive data on retail theft is lacking, researchers say, in part because the term itself encapsulates multiple crimes including burglary, robbery and shoplifting.

Available data from the FBI and the California Attorney General’s Office show burglary and larceny continued a multiyear decline in 2020 both nationally and in the state. Criminology experts anticipate that year-over-year property crime figures will increase in 2021 because the pandemic depressed most crime figures last year.

“One can ask whether this is actually happening at a higher base rate or just getting more media attention because it’s getting shared on social media,” said Dr. Charis Kubrin, professor of criminology, law and society at UC Irvine. “I don’t know the answer to that here.”

What makes the recent mass thefts different from the past?

The recent thefts are unusual in several ways: The large numbers of people involved, the level of group organization, and the presence of weapons like guns and hammers. Police say that the car caravans bringing dozens of people to some of the sites are also a newer development.

Local law enforcement agencies note that the groups are to some extent coordinating on social media but aren’t necessarily centralized. Officials are investigating whether the recent crimes are connected.

When did this start?

Retail organizations and criminologists say large groups of people began noticeably orchestrating retail theft last summer when people capitalized on police-violence protests to commit smash-and-grab thefts in places like Walnut Creek and Oakland. This past summer, a number of high-profile incidents captured viral attention within weeks of each other, heightening fears that such thefts are on the rise.

Are the mass thefts more damaging to stores than other shoplifting or retail burglaries?

Despite the size of groups descending upon businesses, the incidents have elements of spontaneity, said Dr. Jonathan Simon, a UC Berkeley School of Law professor.

“There’s some feeling of these events having a feeling of a flash mob — an outdoor party or indoor party — with the opportunity for very quick, acquisitive, exchangeable-for-money crime,” Simon said. “It can be a fairly superficial, opportunistic response to variables that are highly contingent.”

It’s too early to tell whether the new approaches have led to greater monetary losses for stores. But criminologists say they are concerned about the use of weapons by thieves: In Walnut Creek, three Nordstrom workers were assaulted and another was pepper-sprayed during last weekend’s melee, while a suspected robber was wounded in a shootout during an Oakland marijuana dispensary theft.

Is there actual danger to shoppers? What should they do if they witness group theft?

Generally, law enforcement has advised people not to intervene if they witness shoplifting or a theft and instead alert store or mall security and police, which is what led to recent group-theft arrests in San Jose and Palo Alto. Otherwise, officials say, people should feel safe partaking in the start of the holiday shopping season.

Is this a uniquely Bay Area problem?

Although large retailers and trade organizations contend the Bay Area is a hotspot for retail crime, strings of thefts have been reported in places like Southern California and the Chicago area this fall, sometimes with methods similar to those seen in the Bay Area.

Without comprehensive data, it’s difficult to know how the region compares to other areas. California retailers report that San Francisco remains one of the most expensive markets because of security costs.

Where do the stolen goods go?

Authorities in the Bay Area have long said that large-scale theft rings typically move stolen goods out of the area, whether to other states or overseas.

Santa Clara County District Attorney Jeff Rosen said that fencing operations — which buy the stolen property and resell it — operate in networks his office is “in the process of uncovering and taking down.” Retail associations are also pushing for legislation that would force online marketplaces to more vigilantly to avoid selling stolen items, Michelin said.

Can these trends be attributed to a lack of penalties for shoplifting in California?

Not definitively. In San Francisco, the thefts have driven a debate about prosecution tactics against shoplifting, often mentioning Proposition 47, a 2014 referendum that reclassified shoplifting of items with a total value under $950 to a misdemeanor. The police chief recently pointed to “less consequences” as a factor in theft spikes.

Yet studies examining the effect of Propostion 47 on crime rates — including Kubrin’s — show that the law has had minimal to no impact on violent and property crime.

“We have these new problems on the horizon, we don’t really understand them quite well, and it’s not clear what’s causing them. But Prop. 47 is really not the culprit here,” Kubrin said.

What’s happening to prevent retail theft?

Law enforcement agencies have teamed up to comb social media, increase their presence at storefronts and investigate incidents with surveillance footage. Experts say retail theft can be deterred in the moment with an increased security presence, as was the case in Palo Alto this week when a reported group targeting downtown businesses disbanded in the face of guards and police. Some retailers have also limited their hours and sought more private security.

Looking ahead, criminologists and retailers agree they need to better understand how the groups come together and where exactly the goods are being sold.

“This is a long-term process,” Michelin said. “It’s not an easy fix.”