Erin Piacenti was moving through Manhattan’s Times Square on Monday afternoon, heading home from work, when she stopped briefly in front of a vendor selling sunglasses and baseball hats on the street.

Ms. Piacenti, a 32-year-old vice president at Bank of America, had just started her first week back on the job: Four days earlier, she had posted a photo of herself on social media holding her newborn daughter and standing, beaming, next to her husband.

She wrote about how grateful she was to have spent the past five months on maternity leave and about how her daughter had recently been baptized. The young family had traveled to Long Beach Island, N.J., Rhode Island and Maine.

On Tuesday afternoon, Ms. Piacenti was standing near the vendor on West 43rd Street when she was approached, seemingly at random, by a 49-year-old woman who stabbed her in the abdomen. She was taken to NYC Health and Hospitals, where she was pronounced dead.

Ms. Piacenti was one of two people attacked by the woman, identified as Pamela Cisneros, in quick succession on Monday before police officers shot and fatally wounded the attacker. The other victim, a 68-year-old Rhode Island man named Tak Kam, was expected to recover.

A day later, the authorities were still trying to piece together what had led to the attack.

Ms. Cisneros had had two previous encounters with the police, Police Commissioner Jessica S. Tisch said on Monday.

One occurred on Dec. 20, 2018, when officers found Ms. Cisneros screaming and belligerent on Lexington Avenue near 49th Street in Midtown Manhattan, and determined she was intoxicated, according to an internal police report obtained by The New York Times on Tuesday.

The other happened less than four months later, on March 6, 2019, when Ms. Cisneros attempted to jump in front of a southbound E train at the Union Turnpike-Kew Gardens subway station in Queens, the report said.

The killing of Ms. Piacenti, who attended the University of Pennsylvania and was a graduate of Fordham Law School, shook her co-workers at Bank of America, where she worked in the business selection and conflicts division.

“We are shocked and deeply saddened by the tragic loss of our colleague,” the company said in a statement. “She was a valued teammate who will be greatly missed. Our hearts go out to her family and all of her loved ones.”

She and her husband, Frank Piacenti, lived together in Chester, N.J. Both were 2021 graduates from Fordham Law, according to Jennifer Petra, a spokeswoman at the university.

At Ms. Piacenti’s home on Tuesday, Chester police officers stood outside and warned reporters not to step on the property.

Her parents and husband did not immediately respond to requests for comment.

A woman who identified herself as the grandmother of Mr. Piacenti described his wife as a “beautiful, beautiful girl” who had just given birth only five months earlier. The woman did not provide her name.

In Chester Borough, near Ms. Piacenti’s home in Chester Township, Megan O’Hara, 26, who works in a coffee shop, said residents had been jarred by news of the killing.

“This definitely shakes us up. It’s gotten scarier to go into the city because of things happening like this,” she said.

Many of the borough’s residents commute to New York City, Ms. O’Hara said.

“This feels close to home,” she said. “It’s like a family member passed away.”

Mark Bonamo contributed reporting.