Why would a young mother open fire on a holiday party?

SAN BERNARDINO, Calif. --She was the most unlikely accomplice -- a 27-year-old mother with an infant at home, and now involved in one of the deadliest mass shootings.

Authorities say Tashfeen Malik was clad entirely in black tactical gear, her face obscured by a ski mask. She and her husband Syed Farook fired 65 to 75 rounds in the Inland Regional Center before fleeing in a black SUV.

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This undated photo provided by the California Department of Motor Vehicles shows Syed Rizwan Farook, one of the suspects in the San Bernardino shootings. California Department of Motor Vehicles

Once the car was surrounded, Police Chief Jared Birguan says she fired out of the back taking aim at law enforcement.

"She was engaged in the gun battle with our police officers. There were two shooters at the scene. Yes, she fired rounds," said Birguan. "I think the entire event doesn't make a whole lot of sense."

Police scanner details dramatic shootout with San Bernardino suspects

Authorities know very little about Tashfeen Malik. She was not an American citizen but was here on a K-1 visa according to FBI Special Agent David Bowdich.

"She was here on a Pakistani passport," said Bowdich. He continued, saying it's unusual for a young mother to be involved in a shoot out. "Very unusual."

Police say she had no criminal record, and that she was not on any terrorist watch list.

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    Norah O'Donnell is the anchor and managing editor of the "CBS Evening News." She also contributes to "60 Minutes."