"We're still very confused as a family why she's not still alive," Amy Carey-Jones said late Friday, speaking of her 34-year-old sister, Miriam Carey. "I really feel like it's not justified, not justified."
Another sister, retired New York City police officer Valarie Carey, said there was "no need for a gun to be used when there was no gunfire coming from the vehicle."
The sisters spoke outside Valarie Carey's home in Brooklyn Friday night after traveling to Washington to identify Miriam Carey's body.
Washington's Metropolitan Police Department said in a statement Friday that its Internal Affairs Division is investigating the circumstances that led to the shooting. The Secret Service, Capitol Police and FBI are assisting, the department said.
Secret Service agents and Capitol Police officers both fired shots during the encounter with Carey. Witnesses said Carey hit a Secret Service agent with her car at the White House. A Capitol Police officer was also injured. Both are expected to recover.
A federal law-enforcement official said earlier Friday that Miriam Carey had been under the delusion the president was communicating with her.
Her family said she had been suffering from postpartum depression with psychosis but was not dangerous.
Carey-Jones said her sister had been on medication for postpartum depression but was being taken off the drugs under medical supervision.
"They told her she could get off medication," Carey-Jones said, adding, "There were no indications she was unstable."
But interviews with some of those who knew Miriam Carey, of Stamford, Conn., suggested she was coming apart well before she loaded her 1-year-old daughter into the car for the 275-mile drive to Washington on Thursday.
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."
The official said Carey believed President Barack Obama was communicating to her.
"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.
Valarie Carey questioned the characterizations of her sister's deteriorating mental health and said her Miriam Carey "did not believe the president or any government official was going to do her harm."
After Carey rammed the barricades at the White House, police chased her 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.
A lawyer for Carey's sisters, Eric Sanders, attributed the shooting to the "siege mentality" that has developed because of terrorism.
"We're afraid of everything. We're afraid of ourselves now," Sanders said.
He said the family would do its own investigation, beginning with an autopsy.
Police have said they're confident Carey's actions weren't an accident.
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.
Carey's death was Washington's second deadly incident involving an apparently unstable person in 2½ weeks.
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.
___ Associated Press writers John Christoffersen in Stamford, Eric Tucker, Lauran Neergaard and Adam Goldman in Washington, Michael Melia in Hartford and Jessica Hill in Hamden contributed to this report, along with AP researcher Barbara Sambriski in New York.