STATEN ISLAND, N.Y. -- Prosecutors on Thursday formally dropped all criminal charges against a former Castleton Corners chiropractor who had been accused of harassing and stalking a school crossing guard and sending racist and threatening letters after determining the purported victim had allegedly tried to frame the doctor.

Saying it is in the interest of justice, Assistant District Attorney Uchechukwu Enwereuzor moved to dismiss charges of aggravated harassment, harassment, criminal contempt and stalking contained in three criminal complaints against Danielle Serini during a brief proceeding in Criminal Court.

Meanwhile, on Wednesday, Jennifer Becker, the NYPD school crossing guard at the center of the bizarre episodes, was arrested after a probe revealed she allegedly tried to implicate Serini by sending racist letters, some of which contained a photo of Becker's mixed-race son, as part of an ongoing feud, law enforcement sources said.

Becker, who was busted on charges of aggravated harassment, making an apparently sworn false statement, falsely reporting an incident, endangering the welfare of a child and tampering with physical evidence, was expected to be arraigned later Thursday in Criminal Court.

Mark J. Fonte, Serini's lawyer, waived his client's appearance at Thursday's proceeding.

He said there wasn't sufficient notice for Serini, 39, who was forced to close her practice and move because of the allegations and the publicity they garnered, to make it to court.

"I'm grateful to the district attorney's office for thoroughly investigating this matter," Fonte said outside court. "I can get my client's case dismissed, I can have charges exonerated, [but] it's more difficult to restore her good reputation, her name, her practice, her career."

Crossing guard allegedly framed doc for racist letters 3 Gallery: Crossing guard allegedly framed doc for racist letters

Fonte said part of him wants Becker, 44, prosecuted "to the fullest extent;" however, another part of him "understands that she probably has a serious mental health issue."

"I hope she gets help," he said.

The feud dates back to June of last year when Serini was arrested on harassment and stalking charges.

Serini was accused of spitting at Becker, calling her a derogatory term and flipping her the middle finger in a series of incidents at Victory Boulevard and Slosson Avenue. Becker assisted children from PS 29 and St. Teresa School who cross at that busy intersection.

Becker ultimately obtained an order of protection against Serini.

The charges were ramped up in February after Serini was accused of tossing a lollipop at Becker, repeatedly giving her the middle finger and sticking her tongue out at the crossing guard.

A few weeks later, in March, Serini was accused of penning a series of ugly and threatening letters.

But law enforcement sources now say Becker actually sent at least 12 letters meant to be traced back to Serini to schools, police officers and a reporter with the Staten Island Advance who had covered the chiropractor's original arrest.

Some of the letters even had a photo of Becker's son.

A flier the Advance received contained a photo of Becker's son, a racial slur and an unidentified phone number.

"BLACK LIVES DON'T MATTER," the flyer read. "KILL THIS N----- PIECE BY PIECE AND FEED IT TO THE NYPD."

Another vicious hate-filled letter sent to the 120th Precinct stationhouse and addressed to an officer also allegedly threatened Becker's son.

"My next opportunity will be getting rid of you and that ugly a-- n----- child of the crossing guard. Keep thinking he's safe in school. But when the opportunity hits, it will be bang, bang," the letter read, according to a criminal complaint.

The same cop also received a package a few days earlier containing Dum Dum lollipops with a note stating, "Clue 2." Two hours earlier, a crossing guard received the same lollipop package with a note saying, "Clue 1," the complaint said.