(STAMFORD, Conn., AP) — A woman who was shot to death outside the U.S. Capitol after trying to ram her car through a White House barrier had been under the delusion the president was communicating with her, a federal law enforcement official said Friday.

The woman’s family said she had been suffering from postpartum depression with psychosis.

Miriam Carey’s killing at the hands of police Thursday was Washington’s second major spasm of deadly violence involving an apparently unstable person in 2½ weeks.

Interviews with some of those who knew the Stamford resident suggested she was coming apart well before she loaded her 1-year-old daughter into the car for the 275-mile drive to Washington, D.C.

Carey had suffered a head injury in a fall and had been fired as a dental hygienist, her former employer said.

The federal law enforcement official, who had been briefed about the investigation but was not authorized to discuss it publicly and spoke to The Associated Press on the condition of anonymity, said investigators were interviewing Carey’s family about her mental state and examining writings found in her condominium.

“We are seeing serious degradation in her mental health, certainly within the last 10 months, since December, ups and downs,” the official said. “Our working theory is her mental health was a significant driver in her unexpected presence in D.C. yesterday.”

Carey believed President Barack Obama was communicating to her, the official said.

“Those communications were, of course, in her head,” the official said, adding that concerns about her mental health were reported in the last year to Stamford police.

Stamford police Chief Jonathan Fontneau said his officers had gone to Carey’s home in the past, though not in response to any crime. He gave no details.

The federal official said investigators believe that Carey drove straight to the nation’s capital and that the violence unfolded immediately upon her arrival.

After ramming the barricades at the White House, the apparently unarmed Carey led police on a chase down Constitution Avenue to the Capitol, where she was shot in a harrowing chain of events that led to a brief lockdown of Congress. Carey’s daughter escaped serious injury and was taken into protective custody.

Carey’s sisters said they want to know why she had to die. Valarie Carey, a retired New York City police officer who spoke outside her home in Brooklyn late Friday, said there was “no need for a gun to be used when there was no gunfire coming from the vehicle.”

Attempts to reach police in Washington for comment early Saturday were unsuccessful. Officials previously said circumstances leading to the shooting remain under investigation.

Police have said they’re confident Carey’s actions weren’t an accident.

Carey’s neighbors in Stamford were shocked to learn the driver’s identity and see her gleaming black Infiniti wrecked outside the Capitol in TV footage.

Erin Jackson, her next-door neighbor on the building’s ground floor, said Carey doted on her daughter, Erica, often taking her on picnics.

“She was pleasant,” Jackson said. “She seemed very happy with her daughter, very proud of her daughter.”

Carey’s mother, Idella Carey, told ABC that she began suffering from postpartum depression after giving birth in August 2012 and was hospitalized but had no history of violence.

Experts say symptoms of postpartum depression include lack of interest in the baby; mood swings between sadness and irritability; scary thoughts of something bad happening to the baby; and, in severe cases, suicidal thoughts, but not delusions.

In contrast, a condition known as postpartum psychosis can come with hallucinations, paranoia and desires to hurt the child. But it is extremely rare and does not tend to last for a year, experts say.

“If it’s just a case of postpartum depression, you usually don’t see people hurting others or getting aggressive,” said Dr. Ariela Frieder, a psychiatrist at New York’s Montefiore Medical Center.

She said that some women who appear to have postpartum psychosis actually have a different mental illness, bipolar disorder.

Dr. Brian Evans, a periodontist in Hamden, an hour’s drive northeast of Stamford, said Carey was fired from her job at his office about a year ago but wouldn’t say why. He said Carey had been away from the job for a period after falling down a staircase and suffering a head injury and it was a few weeks after she returned to work that she was fired.

On Sept. 16, a man killed 12 people in a shooting rampage at the Washington Navy Yard before dying in a gunbattle with police. The gunman, Aaron Alexis, a defense industry employee and former Navy Reservist, had complained of hearing voices and said in writings left behind that he was driven to kill by months of bombardment with electromagnetic waves.