HER BROTHER HAS A TERRIFYING THEORY — DID SOMETHING CHANGE BEFORE THE TIMES SQUARE ATTACK?

For years, Patrick Peralta believed his sister Pamela Cisneros had finally found some stability.

After a long history of mental-health struggles, Cisneros had been receiving regular treatment, including medication delivered through injections.

According to Peralta, the treatment appeared to be helping.

She was doing well. She was never aggressive.

Then something may have changed.

“I THINK MAYBE SHE STOPPED”

Peralta told reporters that he wondered whether his sister had stopped receiving the injections she had relied on for years.

He did not know for certain that she had stopped treatment.

And there is no official finding that stopping medication caused, contributed to, or explained the Times Square attack.

But the possibility has become one of the questions surrounding the case.

Peralta said Cisneros had seemed stable for roughly four or five years while receiving regular injections. Her family reportedly saw no warning signs that she was becoming violent.

Her father, Mario Cisneros, separately told The New York Times that Pamela had stopped accepting rides from him to her regular mental-health appointments in April.

She reportedly told him she was fine and did not want to depend on medication.

By August, however, her family believed she was still doing relatively well.

Then came August 31.

THE SWITCH

Police say Pamela Cisneros, 49, carried two kitchen knives into Times Square and attacked two strangers.

Erin Piacenti, 32, a Bank of America vice president and new mother, was fatally stabbed.

A 68-year-old man was also attacked but survived.

Police then confronted Cisneros. Officers attempted to get her to drop the knives and used Tasers, but she continued moving toward them while armed, according to authorities.

Two officers eventually fired their service weapons. Cisneros was taken to Bellevue Hospital, where she died.

The attack has left her family struggling to understand how someone they believed had been stable could suddenly become involved in such a horrifying incident.

WHAT HAPPENED IN THE DAYS BEFORE?

Peralta said the family became concerned when Pamela failed to attend their usual family gathering the week before the attack.

They tried contacting her.

Her mother spoke with her on Saturday.

Pamela reportedly said she was fine.

Less than 24 hours later, she was dead — and another family was mourning the loss of Erin Piacenti.

Peralta said he still could not explain what happened inside his sister’s mind.

“It was like a switch.”

That may be the most haunting question of all.

Was Pamela still receiving her treatment?

Had something changed in the days or weeks before the attack?

Did her mental-health condition play any role at all?

Authorities have not established those answers.

What is known is that a woman her family believed had achieved years of stability suddenly became involved in a deadly attack in the middle of Manhattan.

And now investigators, her family and the public are left trying to understand what changed.