San Bernardino Shooter Tashfeen Malik Joins Small Group of Female Mass Murderers

— -- One of the biggest surprises of Wednesday’s San Bernardino, California, rampage was the involvement of a female shooter.

While some information about the male shooter's background has emerged, far less has been revealed about his partner.

Tashfeen Malik reportedly married Syed Rizwan Farook two years ago, according to Farook's brother-in-law. Police have still not confirmed the nature of their relationship.

The 27-year-old woman was also the mother of an infant, and Council on American-Islamic Relations-Los Angeles Executive Director Hussam Ayloush told ABC News Malik and Farook left their child with one of their parents shortly before the shooting. They reportedly told the grandparent that they had a doctor's appointment.

The FBI said today Malik was in the United States on a Pakistani passport and a K1 "Fiance" visa, meaning Farook would have petitioned for Malik to enter the country and they would have been required to marry within 90 days of her entry, pursuant to U.S. regulations. Officials said Farook had left the country and then returned to the United States with Malik in July 2014.

The couple's specific actions during the attack are still being investigated, but San Bernardino Police Chief Jarrod Burguan today said she was in the back of their rental car during the police chase hours after the shooting, and she was firing one of their two rifles at the police officers as they trailed the rented SUV.

Her alleged involvement in the mass shooting, which left 14 people dead and 21 others injured, adds her to a relatively small list of female mass murderers in the United States.

According to the FBI, there were 160 active-shooter incidents between the years 2000 and 2013. Of those incidents, only six included women as the shooters, meaning 3.75 percent of the time.

Much is still unknown about the motive behind the shooting, though President Obama said this morning "it is possible that this was terrorist-related," but cautioned that there’s no way to know at this point.

ABC News' Jack Date and Lee Ferran contributed to this report.

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