She had a toddler with her, confounding everyone who watched the car crash through barriers and lead police through the heart of high-security Washington.

Law enforcement officials said the black Infiniti was registered to a 34-year-old mother named Miriam Carey, a dental hygienist from Stamford, Conn. They think it was Carey, with her 1-year-old daughter sitting behind her, who flattened barricades outside the White House, struck officers and then set off at high speed down Pennsylvania Avenue.
D.C. police confirmed that the driver was shot and killed after careening around the Capitol grounds and crashing at Second Street NE. There was no sign that she was armed, police said.

Video images showed a young child, her hair in braids, being carried by an officer to the back of a patrol car.

The initial portrait of Carey that emerged suggested a person unlikely to be found in the center of such violence. Carey, according to public documents, friends and family members, had finished college and established a work history as a dental hygienist.

Her sister, Amy Carey, a Brooklyn nurse, was incredulous when she was reached Thursday afternoon and told what had happened.

“That’s impossible. She works, she holds a job,” said Amy Carey, who confirmed that her Stamford-based sister drove a black car. “She wouldn’t be in D.C. She was just in Connecticut two days ago, I spoke to her. . . . .