Philadelphia police say they still aren’t sure if a group of people arrested and accused of defacing buildings in Center City on New Year’s Eve — some carrying flammable or explosive materials — were part of an organized anarchist network, or were more of an informal group of homegrown vandals.

A police statement issued the day after seven people were arrested identified them as part of a “large group of unruly antifa protesters” breaking windows and spray-painting buildings near Ninth and Market Streets around 9 p.m. Thursday. But charging documents obtained by The Inquirer on Tuesday make no mention of any specific group in outlining the alleged crimes by those taken into custody, saying only that each defendant was “acting in concert” with others at the time.

Chief Inspector Michael Cram said Monday that he believed the group’s behavior appeared inspired by actions often associated with antifa, a far-left group often accused of an array of antigovernment misdeeds. Cram acknowledged, however, that none of those arrested had been on law enforcement’s radar previously, and said that although the city has experienced similar acts of vandalism recently — including at a camp for people experiencing homelessness — it can be difficult to determine how or if any of those incidents might be linked to any broader group, or even a loosely connected movement.

“Here’s the problem with it,” Cram said. “We don’t know who is actually doing it. Are they just ‘wannabes,’ or are they officially affiliated? We really don’t know.”

Lawyers for those whose attorneys were named in court filings did not return requests for comment. Each was released on bail after being arraigned, according to court records.

Police said last week that officers made two sets of arrests for vandalism and arson around 9 p.m. Thursday.

Four people were arrested at Ninth and Market Streets and accused of throwing bricks through the windows of the Robert Nix Federal Building, police said: Adam McVicker, 25, of Coatesville; Dustin Callahan 24, of Farmingdale, N.J.; Allison Donohue, 23, of Wallingford; and Josey Augustine, 31, of Royersford.

Three others were arrested at Sixth and Sansom Streets, police said: Jacob Robotin, 25, of Willow Grove; Sydney Miller, 22, of Philadelphia; and Meredith Tooker, 26, of Philadelphia. They were found with spray paint on their clothes and backpacks containing what charging documents called “explosive materials” and an “improvised incendiary device” — including bottles or jars filled with flammable liquids, one of which had a fuse, and a white powder that was labeled as a fire starter.

Each was charged with criminal mischief and related counts. Police said the damage to the building was estimated at $3,000.

A review of the defendants’ social media activity showed little that would seem to connect them to each other outside of a shared left-leaning worldview.

Still, since the arrests, fund-raising pleas circulated in activist circles to help them make bail.

Several of those arrested have participated in social justice protests last year, like Augustine, who was present at last summer’s homeless encampment along the Benjamin Franklin Parkway and at protest events led by the activist group Refuse Fascism Philly. Augustine follows Berks County Antifa’s Facebook page, according to their profile on the platform.

Some, such as Miller, a Temple University student, have turned their Facebook and Instagram profiles into platforms for what she has described as leftist, “not liberal,” posts railing against racism, police violence, and gentrification.

Notably, though, none of them appears to have obvious social links to each other or antifa.

Nonetheless, activist groups online have increasingly urged supporters to avoid posting on social media for fear of law enforcement using it to monitor their activities.

Staff writer Oona Goodin-Smith contributed to this article.