A day after looters smashed-in retailer’s windows, carried away loads of high-end merchandise and overwhelmed police officers in downtown Chicago, Mayor Lori Lightfoot says the violence was an organized raid and not a demonstration of angry protest.

“When people showed up on Michigan Avenue in the downtown area with U-Haul trucks and cargo vans, and sophisticated equipment used to cut metal, and the methods that were used, and how quickly it got spun up… that wasn’t any spontaneous reaction,” Lightfoot told TIME in her fifth-floor offices at Chicago’s City Hall on Tuesday.

The chaos that unfolded Sunday night, and into the predawn hours Monday, was initially blamed on a police shooting in the city’s southside Englewood neighborhood. News of the incident—along with misinformation that a minor had been shot—pinballed on social media, resulting in “caravans” of cars headed north downtown, Lightfoot says.

“To be sure, there are people that did join in that were motivated by lots of different reasons, and certainly were motivated by social media posts encouraging people to come downtown,” Lightfoot says. “But the core of what happened — that’s organized criminal activity… It was a planned attack.”

For three hours that night, Chicago was under virtual siege. Hundreds of people flooded the streets. Looters broke into buildings and came out with armfuls of jewelry, clothes, electronics and other goods. The 911 switchboard was swamped with 1,800 calls between midnight and 3 a.m., a figure that’s typically in the teens at those hours. Lightfoot says the looters knew that police staffing would be low that early Monday morning and therefore picked “the moments where they feel like they have the best opportunity to make a move.”

The aftermath seen at the store Nordstrom on Aug. 10, 2020, following a night of unrest in Chicago. | RMV/Shutterstock

The city’s Magnificent Mile and other shopping districts were hit with widespread theft, vandalism and destruction. Many of the businesses were big-name retailers like Gucci, Nordstrom and Apple. Some were looted just six weeks earlier amid the violent unrest that erupted after George Floyd, an unarmed black man, died in Minneapolis police custody in May. And all were struggling to deal with the economic impact of the COVID-19 pandemic.

Chicago, like many other U.S. cities, is in the midst of a surge in violent crime. Last month, 573 people were shot in America’s third largest city — at least 58 of them juveniles. There have been 430 recorded homicides through July, which represents a 51% increase over the same period last year. Compare that to New York City, for example, which had just 237 murders, despite having nearly three times the population.

In recent days, the Chicago Police Department has instituted 12-hour shifts and canceled days off for all officers until further notice. On Monday, the department sent 400 officers downtown. Expressway exits were closed and nearly every bridge was raised to seal off the area. By dawn, it was clear Chicago was an American city in distress. Shattered glass carpeted sidewalks. Trash billowed down major streets. Police stood guard in riot gear on corners.

Lightfoot says authorities have yet to identify ringleaders or individuals who she believes strategized the violence. A task force of police detectives, FBI agents and officials with the U.S. Attorney’s office are now busy collecting and analyzing hundreds of hours of security camera footage to identify those involved.

“We’re still going through lots and lots of video tape,” Lightfoot says. “But people were able to fairly quickly take out cash registers, ATM machines, cut through metal grate, and to get beyond and behind security systems that are pretty sophisticated. That’s not your average looter.”