Motive mystery over woman killed in US Capitol drama

Miriam Carey, who allegedly rammed a barrier at the White House in a black Infiniti two-door coupe was shot and killed

Investigators have sought to find out why a 34-year-old mother from Connecticut led police on a high-speed chase through Washington only to be shot and killed outside the US Capitol.

Miriam Carey, a dental hygienist, allegedly rammed a barrier at the White House in a black Infiniti two-door coupe, then sped down Pennsylvania Avenue with her year-old baby girl at her side.

The infant was placed in protective custody in a Washington children's hospital in the aftermath of a drama that triggered a lockdown of the Capitol on day three of a US government shutdown.

Police who searched her home in Stamford, Connecticut found a crib, children's toys and baby bottles, but no weapons or anti-government material, the Hartford Courant newspaper reported.

Carey's mother Idella Carey told ABC News that her daughter had "no history of violence" and that it was a mystery why she was in the nation's capital in the first place.

"She had post-partum depression after having the baby" in August last year, she said. "A few months later, she got sick. She was depressed... She was hospitalised."

Several US news media yesterday quoted a law enforcement source who they did not name as saying that Carey had had delusional thoughts that President Barack Obama was communicating with her and that she was under electronic surveillance.

CBS News said Carey had sustained a head injury in a fall in April 2012 for which she got hospital treatment. It also said she had been fired from her job at a dental clinic after an argument over a handicapped parking spot.

On Facebook, there was an outpouring of anger directed at police on a memorial page for Carey created by a friend in the wake of the incident.

"I hope her family sues the Capitol Police Dept," wrote one woman, referring to the well-armed specialised force that patrols the Capitol building and its surroundings.

"Why couldn't they shoot the tires of the vehicle? Deadly force with a child in the car? I just can't understand this."

Officials said the chase began at the outer perimeter of the White House security cordon, where the suspect's car struck a barrier and a uniformed Secret Service officer.

No shots were fired initially, but agents gave chase as the car sped away. As the vehicle closed in on the Capitol, the seat of Congress, it was cornered by police vehicles and armed officers on foot.

A college graduate and registered dental assistant, she worked at Advanced Periodontics in Hamden, Connecticut, which in 2011 published a newsletter -- still on its website yesterday -- raving about her people skills.