L to R: Mercer County Prosecutor Angelo Onofri, Kathleen Petrucci, and Jennifer Downing-Mathis

Kathleen Petrucci has been promoted to deputy first assistant prosecutor for Mercer County and was sworn in last week by Judge Peter Warshaw at the Mercer County Criminal Courthouse.

Petrucci began her career as an assistant prosecutor in the Mercer County Prosecutor’s Office in September 1999. During her 24 years with the office, she has been assigned to the trial unit, gang unit, project safe neighborhoods unit, juvenile unit, grand jury unit, Mercer County Narcotics Task Force, internal affairs unit, and the Mercer County Homicide Task Force. She has served as chief of the juvenile unit and chief of the gang unit. After four years as a trial team leader, Petrucci was assigned to the special investigations unit and served as its chief from 2016-2018. She was also cross-designated as a special assistant U.S. attorney, and assigned to the U.S. Attorney’s Office in 2018-2019 to screen and adopt state drug and gun crimes from Mercer County and prosecute those defendants federally in U.S. Magistrate Court. Most recently, she has been the senior assistant prosecutor supervising the Mercer County Homicide Task Force.

During her career in Mercer County, Petrucci has conducted numerous jury trials arising from homicides, aggravated assaults, firearms possessions, and drug distributions. Trials have included the attempted murder case of State v. Billy Heisler, who was convicted in 2012 of the attempted murder of an off-duty Mercer County Sheriff’s Officer and sentenced to 50 years in New Jersey State Prison, and more recently the double-murder case of State v. Treizon Thompson, who was convicted in December 2022 of the murders of two rival gang members.

In addition to her prosecutorial duties, Petrucci has taught firearms law, controlled dangerous substance law, and juvenile justice at the Mercer County Police Academy and the New Jersey State Police Academy, and has guest lectured at The College of New Jersey and Mercer County Community College.

While Petrucci will continue to prosecute homicide cases, officials said her responsibilities in her new role will expand to include general oversight of major crimes, special investigations, and appellate units, as well as assisting with formulating policy and overseeing investigations. She has served as an administrative assistant prosecutor since September 2021.

Petrucci graduated from Bethany College in West Virginia in 1992 and from Seton Hall University Law School in 1998. Prior to joining the prosecutor’s office, she was a law clerk for Judge Paul Koenig from 1998 to 1999.