Updated

A Pennsylvania woman pulled out a handgun and threatened a fellow passenger during an argument onboard a public bus, but a third passenger is being hailed as a hero for breaking up the confrontation before it escalated further, police said.

The altercation onboard the Southeastern Pennsylvania Transportation Authority bus in Upper Darby, just outside Philadelphia, was captured on video.

The woman was arrested after getting off the bus and a gun was found in her purse, police said. Cordelia Chisholm, 58, of Yeadon, was being held on charges of aggravated assault and other counts. It could not immediately be determined if Chisholm had an attorney, and a telephone number for her could not be located.

Upper Darby police Superintendent Michael Chitwood told the Delaware County Daily Times that a 22-year-old woman talking on a cell phone Thursday evening bumped into Chisholm, who pulled out the gun and threatened her.

A shouting and pushing match ensued before a third passenger, an unidentified man, stepped in and quelled the dispute as Chisholm held the gun to the victim's stomach, Chitwood said.

"If it weren't for this guy, who knows how many would have been shot if the gun went off," Chitwood said during a news conference Monday, estimating that there were about 30 people on the bus. "The Good Samaritan walked into harm's way and separated these two individuals. He did in fact save lives."

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Information from: Delaware County Daily Times, http://www.delcotimes.com