More than a dozen people were arrested after stores were looted when a large crowd gathered in Philadelphia's Center City district Tuesday night, police said.

The looting began shortly after the conclusion of peaceful protests against a judge's decision to dismiss all charges against a former Philadelphia police officer, Mark Dial, in the fatal shooting of 27-year-old Eddie Irizarry on August 14, authorities said. The city's police commissioner said he believes the looters were "opportunists" that were not directly connected to the protests.

"This had nothing to do with the protests. What we had tonight was a bunch of criminal opportunists take advantage of a situation," Commissioner John Stanford in a late-night news conference.

Police started getting calls around 8 p.m. from businesses reporting they were being broken into or getting ransacked, Stanford said.

Officers responded to the stores, arresting around "15 to 20 people" and working to disperse growing crowds of "juveniles and young adults," Stanford said.

"We were told at one point that crowd got as large as maybe 100 or so that were just making their way through Center City area," the commissioner said.

Reports of looting began in the Center City area, then continued in other neighborhoods, according to Stanford.

"We're investigating that there was possibly a caravan of a number of different vehicles that were going from location to location," the commissioner told reporters.

It appears looters came from different parts of the city, Stanford said, adding that officers still were determining where they came from and how the different vehicles may be connected.

Stanford said it's still unclear how many businesses were hit Tuesday, but said stores targeted included clothing and sneaker shops, high-end stores, wine and spirit stores and pharmacies.

Cell phone video obtained by CNN shows several people in hooded sweatshirts running in and ransacking an Apple store Tuesday night. Different video captured officers detaining several people outside a Lululemon store, where items of clothing could be seen littering the ground.

Elsewhere, officers were seen outside a Foot Locker store, where the window was smashed and merchandise was strewn around the floor, video from CNN affiliate KYW showed.

Police still were responding to 911 calls related to the looting as Stanford briefed the media Tuesday night, but the commissioner said he believes officers "have it contained."

Investigators will be looking through video from the area to make additional arrests, Stanford said.

"We made arrests and we will continue to make arrests until we have all of the individuals, or a number of the individuals, that have been responsible for what we've seen tonight in custody," he said.

The reports lootings in Philadelphia come as a wave of retailers -- both large and small -- say they're struggling to contain store crimes that have hurt their bottom lines.