Cambridge police are “aggressively” investigating a Sept. 24 incident in which about 20 teens faced off outside the Francis J. Frisoli Sr. Youth Center, City Councilor Tim Toomey said Monday night.

After at least three speakers at the councilors’ Oct. 5 meeting referred to the incident, Toomey and fellow City Councilor Kenneth E. Reeves contacted police, they said near the end of a council meeting held in Sullivan Chambers in City Hall.

They were compelled by testimony such as that of area resident Claire Koen, who told them, “I’ve never seen such violence. I was petrified,” in recalling the September evening incident. Other people who’d been on the scene in September — including council candidate Charles Marquardt — said mainly that youths had been outside the 61 Willow St. center exchanging insults and racial epithets and beginning to push and shove each other when police were called.

While Reeves said he hadn’t been able to get many specifics of the investigation, Toomey was able to share that, according to police, “some individuals from outside the city were trying to instigate” a fight, and that officers “are aggressively working” on the case. The investigation was said to include discussion with law enforcement officials from outside the city.

While Marquardt and attorney Richard Clarey said Oct. 5 that they’d called police and were concerned it took officers so long to respond, Toomey said Monday that there was no record of police getting a call about the incident.

On Oct. 8, police spokesman Officer Frank Pasquarello said in a telephone interview that there was no report on the incident because no one had filed a complaint, but he would try to find an officer who’d gone to the scene of the altercation to fill in details about what happened. Pasquarello was not in contact after that.