An investment banker from Syosset says she was wrongfully arrested by Nassau County police for stealing a diamond sapphire ring from Roosevelt Field mall despite having evidence that proved her innocence, a federal lawsuit alleges.

Angela Bianco, 49, was accused of taking the $2,499 ring from Helzberg Diamonds on Oct. 27, 2014, even though surveillance video showed the crime was committed by a much younger woman who “in no way resembles” Bianco and a male accomplice, the lawsuit filed on Wednesday claims.

After an investigation by the Nassau County district attorney’s office, prosecutors dropped all charges against Bianco on Feb. 5, 2015, court records show.

“The people have done an exhaustive investigation in this case,” Assistant District Attorney Alexander Lev told Nassau County Judge Francis Ricigliano. “That investigation has included a review of security video in which . . . it does not appear that the defendant who was arrested committed the crimes alleged.”

Police declined to comment on the lawsuit, and they would not say if any arrests were made in the case.

The lawsuit alleges police did not have a warrant to enter Bianco’s home or arrest her, but did both on Nov. 21, 2014. Two officers arrived in unmarked cars, wore plain clothes, and did not identify themselves as police, court papers say.

Bianco, who was home with her parents and sister at the time, “believed the individuals banging on the door were potential burglars, in part because they were not in uniform, never identified themselves, did not display their shields, and their behavior was unprofessional,” according to the lawsuit.

advertisement | advertise on newsday

Bianco, who had no prior arrest record, later said she could show police sales receipts proving she was actually at a different store in the mall, New York & Company, at the time of the ring theft, but they booked her anyway, the suit alleges.

She was charged with grand larceny, criminal possession of stolen property, identity theft and criminal impersonation, records show. She declined requests for an interview.

But Bianco’s attorney, Anthony Grandinette of Mineola, said that “even an elementary schoolchild would have easily concluded that Angela Bianco was clearly innocent.”

He added: “Perhaps more disturbing is, despite her attempts to explain to the detectives that they were making an egregious mistake, they taunted, ridiculed and mocked her. Had police just taken a moment to listen rather than ridicule, these events would have never transpired.”

Nassau County, the county police department, Nassau police Det. Gennaro DeStefano, Nassau police Lt. Vincent Boden and 10 unidentified police department employees are named in the suit.

@Newsday

According to the suit, Det. DeStefano and Lt. Boden, along with other officers at the Third Precinct, “mistreated Bianco and violated laws pertaining to holding facilities and prisoner safety proscribed by the Nassau County Police Department and the New York State Department of Corrections.”

“For example, they mocked Bianco, raising their voices and screaming out, ‘I didn’t do it, I didn’t do it, I’m innocent,’ ” according to the suit.

Bianco, who had surgery in her armpit as part of treatment for breast cancer, told officers the position in which they’d handcuffed her “caused her immense pain,” the suit states.

But police ignored her complaints, the suit alleges.

They also questioned her after she had “unequivocally” invoked her right to counsel, according to court papers.

advertisement | advertise on newsday

That same day she was arrested, Bianco was involuntarily taken to Nassau University Medical Center for a psychiatric evaluation, according to the lawsuit.

“At the hospital, Bianco explained to the medical personnel that she was not crazy, but rather the police were arresting her for something she did not do and that they refused to listen to her,” the lawsuit alleges.

Bianco’s suit seeks a jury trial and unspecified damages, claiming the false allegations damaged her career as a mergers and acquisitions investment banker.

According to the suit, a man and woman who appeared to be in their late teens or early 20s were the ones who actually stole the ring.

The woman asked the store clerk at Helzberg Diamonds to see the ring, and a female clerk handed it to her, the suit states. When the clerk turned her back to the duo, the man took the ring and left the store, the lawsuit alleges.

advertisement | advertise on newsday

His female accomplice left a short time later, leaving a stolen credit card and driver’s license on the counter — neither of which belonged to Bianco, the suit states.

Later, prosecutors discovered surveillance video that showed Bianco had been in a different store, New York & Company, at the exact time of the theft — just as her receipts had shown, according to the suit.

Bianco left Roosevelt Field mall about 20 minutes after the ring-stealing duo left Helzberg Diamonds, the lawsuit alleges.

At other points in the night, Bianco visited a Victoria’s Secret store, Phil’s Pizzeria & Restaurant on Jericho Turnpike in Syosset, and New York Sports Club on Ira Road in Syosset, records show.

At no point that day did she visit Helzberg Diamonds, the lawsuit says.