Officers spotted the large group around 8:30 p.m. Thursday at Robert Nix Federal building on the 900 block of Market Street where windows were smashed.
A 25-year-old man, identified as Adam McVicker of Coatesville, Pa., was seen throwing a brick through windows into the federal building, police said. He fled with a 24-year-old man and two 23-year-old women, all of whom were arrested. Damage to the building was estimated at about $3,000.
Officials said several people ran, but not before police made three arrests.
The vandals then hit the Federal Detention Center at 7th and Arch streets with Antifa-related graffiti, police said.
Three people, a 25-year-old man and two women aged 22 and 26, were arrested. The suspects had spray paint on their clothing and markers in their possession, police said.
Police said the man, identified as Jacob Robotin of Willow Grove, Pa., was carrying a green military-style backpack that contained a black plastic bag containing a glass jar with a fuse going into the bottle giving off a "strong flammable odor." The bag also contained a plastic container with a white powdery substance labeled "Fire Starter," police said.
The 22-year-old woman, identified as Sydney Miller of Philadelphia, had bottles with unknown liquids, some of which had "a chemical smell," police said.
The following seven people are facing charges:
- Adam McVicker, a 25-year-old male from Coatesville, PA
- Dustin Callahan 24-year-old male from Farmingdale, NJ
- Allision Donohue 23-year-old female from Wallingford, PA
- Josey Augustine, 31-year-old female from Royersford, PA
- Jacob Robotin, a 25-year-old male from Willow Grove, PA
- Sydney Miller, 22-year-old female from Philadelphia
- Meredith Tooker 26-year-old female No residence given.
Responding officers believe the group had more plans for the night.
"During a search, they recovered Molotov cocktails and some other devices which have not been identified," Philadelphia Police Chief Inspector Mike Cram said.
The Associated Press contributed to this report.