A tax preparer has been arrested for stalking and threatening to harm an assistant district attorney in the Manhattan DA’s office.

Jack Chang, 54, president of Unitax Planners in Jackson Heights, Queens, was arrested on charges of coercion, placing a false bomb or hazardous substance, stalking and aggravated harassment. He was arrested after Assistant DA Gilda Mariani, chief of the money laundering and tax crimes unit in Manhattan DA Robert Morgenthau’s office, received two threatening letters from Chang on June 9.

Mariani had been handling a prosecution of Chang on charges of grand larceny and a scheme to defraud his clients of more than $80,000 when she started receiving threatening letters. She had previously supervised a prosecution of Chang, in which he was convicted and sentenced to prison for stealing more than $940,000 from at least 30 clients between 1988 and 1992.

One of the threatening letters was sent to Mariani’s husband at their home, and another was addressed to her office. The letter delivered to her home contained a white powder, which was determined to be cornstarch based on a preliminary analysis. Both letters threatened Mariani with physical harm and death, but did not include the sender’s name.

“I finally got my 9 mil gun and I am insane, you are responsible for my insanity, and I will make sure that you get at least one for each and every year I spent incarcerated,” said one letter.

Investigators focused on Chang as the writer of the letters, in part because he had been in the DA’s office on both June 4 and June 5, in connection with the grand larceny and scheme-to-defraud prosecution that Mariani was conducting.

Investigators believe they have obtained substantial incriminating evidence against Chang. On June 16, they seized a bag of trash from in front of his house and found what appeared to be a draft of the threatening letters sent to Mariani. During the execution of a search warrant at his home, they discovered more incriminating evidence, including a computer printout of Mariani’s biography, as well as another threatening letter directed toward her.

The letter found at Chang’s home stated, in part, “You will be captured and before you are sent to hell you will taste hell on earth.” Investigators also seized a computer printer and mailing labels resembling those affixed to the letters received by Mariani.

Chang faces up to seven years in prison on the coercion charge, up to four years on the hazardous substance charge, and one year each on the stalking and aggravated harassment charges.