A voicemail from a detective, a business card left in your door, or a letter on Mercer County Prosecutor’s Office letterhead all mean the same thing: you have become part of a criminal investigation. You may be a witness, a person of interest or the target. What you do in the next few days can decide whether charges are ever filed.
The Mercer County Prosecutor’s Office (MCPO) is the chief law enforcement agency in the county. It has about 200 employees and is led by Prosecutor Janetta D. Marbrey, who took office in December 2024. Trenton is also the state capital, so people here are sometimes contacted by state agencies instead, including the Attorney General’s Office and the New Jersey State Police. The advice below applies to all of them.
Mercer County Prosecutor’s Office: Basic Information
| Office | Mercer County Prosecutor’s Office |
| Address | Mercer County Courthouse, 209 South Broad Street, Trenton, NJ 08650 |
| Prosecutes | Indictable crimes (first through fourth degree) committed anywhere in Mercer County’s 12 municipalities |
| Cases are heard at | Mercer County Criminal Courthouse, 400 South Warren Street, Trenton |
| Our nearest office | 100 Horizon Center Boulevard, Hamilton, NJ 08691 · (732) 858-6959 |
Before you return a detective’s call, call us at (732) 858-6959. A short conversation with a lawyer first costs you nothing and can protect you a great deal.
How Mercer County Investigations Usually Start
The MCPO works with local police departments across the county and with federal and state partners. Investigations that reach the Prosecutor’s Office tend to fall into a few categories:
- Violent crime and shootings, many of them in Trenton, often handled with the Trenton Police Department and the office’s homicide and major crimes investigators
- Drug and gang investigations involving wiretaps, controlled buys and search warrants
- Sexual offenses and child abuse, investigated by special victims detectives, sometimes after a report from a school or DCPP
- Financial and public-corruption cases, including theft from employers, government contracts and nonprofits
- Cyber crime and child exploitation, often starting with a tip about an IP address
- Campus-related incidents involving students at Princeton University, The College of New Jersey or Rider University
If a Mercer County Detective Contacts You
Detectives are trained to sound casual. “We just want to clear a few things up” or “You’re not in trouble, we just need your side” are common openers. The safest response is polite and short:
- Take the detective’s name, unit and phone number.
- Say you will have your attorney call them back.
- Do not explain, deny or “set the record straight.” Anything you say can be used, and a false or inconsistent statement can become its own problem.
- Do not agree to come to the office on South Broad Street for a “quick chat” on your own.
New Jersey gives you the right to remain silent and the right to a lawyer. Using those rights is not evidence of guilt. A defense attorney can find out why the detective is calling, whether you are a witness or a target, and whether speaking would help or hurt.
Letters, Subpoenas and Search Warrants
Target letters
A target letter tells you that the State considers you a likely defendant and may invite you to testify before the grand jury. Testifying without counsel is almost never in your interest. A lawyer can contact the assigned assistant prosecutor and sometimes resolve the matter before indictment.
Grand jury subpoenas
Mercer County grand juries sit in Trenton. A subpoena for testimony or records is a court order and cannot be ignored. Your lawyer can negotiate the scope, raise privileges and, in some cases, arrange for you to produce documents instead of appearing.
Search warrants
If detectives arrive with a warrant, do not interfere, and do not consent to anything beyond what the warrant allows. Ask for a copy of the warrant and the inventory of seized items, and call a lawyer right away. Phones and computers seized in Mercer County are typically sent for forensic extraction, which can take months.
What Happens After Charges Are Filed
An investigation does not have to end in an indictment. The chart below shows the main points where a case can leave the system, and where a defense lawyer can push it toward the exit.
Simplified paths of a Mercer County investigation. Pretrial Intervention requires prosecutor consent.
Once a complaint is signed, the case moves to the Criminal Courthouse on South Warren Street. If the person is held, they go to the Mercer County Correction Center, and a first appearance must happen within 48 hours. Assistant prosecutors then review the case for grand jury presentation, downgrade to municipal court, or a pre-indictment plea offer.
Mercer County defendants may also be eligible for diversion:
- Pretrial Intervention (PTI): a supervised program that ends in dismissal. The prosecutor must consent, and applications generally have to be filed early in the case.
- Recovery Court: an intensive, court-supervised treatment program for people whose charges are tied to substance use or mental health issues.
- Conditional discharge or conditional dismissal: for certain lower-level and municipal court charges.
Early defense contact with the MCPO often decides which of these paths is available.
How the MCPO Uses Detention Motions
How a prosecutor’s office uses its power to ask for pretrial detention says a lot about how it approaches cases. New Jersey Judiciary statistics for 2024 show a distinct pattern in Mercer County:
- Volume: The MCPO filed 733 detention motions in 2024, up from 702 in 2023.
- Withdrawals: It withdrew or dismissed 290 of those motions (39.6 percent), nearly double the statewide rate of 20.8 percent. Many withdrawals follow a defense presentation of a release plan or new information.
- Grant rate: When a judge decided the motion, the State won 73.1 percent of the time in 2024, up from 64.1 percent in 2023 and above the 62.1 percent state average.
Mercer County detention motion outcomes, 2023 and 2024, as a share of all motions filed. Source: NJ Courts, Criminal Justice Reform Statistics.
The takeaway for anyone facing a serious charge in Mercer County is simple. The best time to influence a detention decision is before the hearing, when the assistant prosecutor is still deciding whether to press the motion. A lawyer who calls early with verified information about housing, employment and treatment can sometimes get a motion withdrawn entirely.
Mistakes That Make Mercer County Cases Worse
In our experience, these are the missteps that most often turn a manageable investigation into a serious prosecution:
- “Clearing things up” with a detective. Voluntary interviews often supply the only proof of intent or knowledge the State has.
- Consenting to a phone search. A phone holds years of messages, photos and location data. Consent waives the warrant requirement.
- Contacting the complaining witness. Even an apology can be charged as witness tampering or violate a no-contact order.
- Posting about the case. Social media posts are routinely collected and used at trial and at detention hearings.
- Ignoring a subpoena or letter. Missing a grand jury date or a scheduled appearance can lead to a warrant.
- Waiting to hire counsel. Pretrial Intervention applications, pre-indictment negotiations and evidence preservation all have short windows.
Protecting Evidence That Helps You
The prosecutor’s job is to build a case. Your lawyer’s job includes making sure evidence that helps you is not lost. In Mercer County cases, that often means acting quickly to preserve:
- Surveillance video from businesses along Route 1, Route 33 or in downtown Trenton, which many systems overwrite within days or weeks
- Body-worn camera and dash camera recordings from local police departments
- Phone records, ride-share receipts and location data that support an alibi
- Names and contact information of witnesses before they become hard to find
A preservation letter or subpoena early in the case can make the difference between a defense and a guess.
County or State Investigation?
Because Trenton is home to state government, residents and public employees are sometimes contacted by the Attorney General’s Office of Public Integrity and Accountability, the Division of Criminal Justice or the State Police rather than the MCPO. The rules are the same: do not answer questions without counsel. A lawyer can identify which agency is involved and what it is investigating.
Frequently Asked Questions
Can I just call the detective back myself to find out what it is about?
You can, but detectives often use that call to begin questioning. It is safer to let your lawyer make the call.
I live in Pennsylvania. Can Mercer County detectives charge me?
Yes. If the alleged offense happened in Mercer County, the MCPO can file charges and seek extradition. Many Bucks County residents are investigated here.
Will talking help me avoid charges?
Sometimes a carefully prepared statement or a proffer through counsel does help. That decision should be made with a lawyer who has reviewed the situation, not on the spot.
Does the MCPO handle Princeton and Hopewell cases too?
Yes. The Mercer County Prosecutor’s Office handles indictable crimes in all of Mercer County’s municipalities, including Princeton, Hopewell, West Windsor and East Windsor, not just Trenton.
What if I receive a target letter from the Attorney General instead?
Treat it the same way. Have a New Jersey defense lawyer contact the assigned deputy attorney general before you respond or appear.
Talk to a Mercer County Criminal Defense Lawyer
Keith Oliver, William Proetta and Brett Rosen regularly handle investigations and prosecutions brought by the Mercer County Prosecutor’s Office. Call (732) 858-6959 or contact us online for a confidential consultation. See also our pages on the Mercer County Correction Center and Mercer County warrants.
More Mercer County Criminal Defense Guides
- Mercer County Superior Court criminal cases
- First appearances and detention hearings in Mercer County
- Mercer County Correction Center (county jail)
- Clearing a warrant in Mercer County
- Mercer County criminal defense lawyers