A federal law enforcement official says 34-year-old Miriam Carey, who was killed by police Thursday after trying to drive through barricades outside the White House, was delusional and believed the president was communicating with her.

The official, who had been briefed about the investigation, spoke on condition of anonymity because the person was not authorized to speak publicly about the ongoing investigation. The official said Carey had been in a deteriorating mental state since December.

Investigators who have been interviewing Carey's family about her mental condition believe she drove directly to Washington immediately before Thursday's car chase, officials said.

Carey's mother earlier said her daughter suffered from postpartum depression.

The harrowing chase unfolded between two U.S. landmarks, briefly shuttered the chambers where federal lawmakers were debating how to end a government shutdown and stirred fresh panic in a city where a gunman two weeks ago killed 12 people.

Miriam Carey Capitol Hill car chase suspect

ABC News reported that Miriam Carey was a 34-year-old dental hygienist who suffered from postpartum depression. (Advanced Periodontics of Hamden)

Two law enforcement officials identified the driver as 34-year-old Carey, of Stamford, Conn.. She was travelling with a one-year-old girl who avoided serious injury and was taken into protective custody. The officials spoke on condition of anonymity because they were not authorized to discuss an ongoing investigation.

Carey's mother, Idella Carey, told ABC News on Thursday night that her daughter began suffering from postpartum depression after giving birth to daughter Erica last August.

"A few months later, she got sick," she said. "She was depressed.... She was hospitalized."

Idella Carey said her daughter had "no history of violence" and she didn't know why she was in Washington on Thursday. She said she thought Carey was taking Erica to a doctor's appointment in Connecticut.

Police said there appeared to be no direct link to terrorism and there was no indication the woman was even armed. Capitol Police Chief Kim Dine, whose officers have been working without pay as a result of the shutdown, called it an "isolated, singular matter."

Still, tourists, congressional staff and even some senators watched anxiously as a caravan of law enforcement vehicles chased a black Infiniti with Connecticut licence plates down Constitution Avenue outside the Capitol and as officers with high-powered firearms canvassed the area. The House and Senate both abruptly suspended business, a lawmaker's speech cut off in mid-sentence, as the Capitol Police broadcast a message over its emergency radio system telling people to stay in place and move away from the windows.

The woman's car at one point had been surrounded by police cars and she managed to escape, careening around a traffic circle and past the north side of the Capitol building. Video shot by a TV cameraman showed police pointing firearms at her car before she rammed a Secret Service vehicle and continued driving. Metropolitan Police Chief Cathy Lanier said police shot and killed the woman a block northeast of the historic building.

In Connecticut, the FBI served a search warrant in connection with the investigation and police cordoned off a condominium building and the surrounding neighbourhood in the shoreline city.

The chain-of-events began when the woman sped onto a driveway leading to the White House, over a set of barricades. When the driver couldn't get through a second barrier, she spun the car in the opposite direction, flipping a Secret Service officer over the hood of the car as she sped away, said B.J. Campbell, a tourist from Portland, Oregon.

Then the chase began.

One Secret Service member and a 23-year veteran of the Capitol Police were injured. Officials said they are in good condition and expected to recover.

Congressman Michael McCaul, who said he was briefed by the Homeland Security Department, said he did not think the woman was armed. "There was no return fire," he said.

A few senators between the Capitol and their office buildings said they heard the shots.

"We heard three, four, five pops," said Democratic Sen. Bob Casey. Police ordered Casey and nearby tourists to crouch behind a car for protection, then hustled everyone into the Capitol.

Others witnessed the incident, too.

"There were multiple shots fired and the air was filled with gunpowder," said Berin Szoka, whose office at a technology think tank overlooks the shooting scene.

The shooting comes two weeks after a mentally disturbed employee terrorized the Navy Yard with a shotgun, leaving 13 people dead including the gunman.

Before the disruption, lawmakers had been trying to find common ground to end a government shutdown. The House had just finished approving legislation aimed at partly lifting the government shutdown by paying National Guard and Reserve members.

Capitol Police on the plaza around the Capitol said they were working without pay as the result of the shutdown. A spokesman for House Majority Leader Eric Cantor said a bill to pay them was under consideration.

washington capitol shooting map420

A map of Washington, D.C., showing points of the Oct. 3 2013 car chase and shooting. (CBC)