Prosecutors say three 18-year-olds assaulted a classmate in a minivan after the party.
ROSELLE, Ill. — Three 18-year-olds accused of sexually assaulting a female classmate after a Saint Viator High School graduation party in Roselle are headed to court in January, after prosecutors said a judge ordered one defendant held before trial and released two others under strict conditions.
The case has unfolded in stages, beginning with a report to police in mid-June and culminating with arrest warrants issued Dec. 17, 2025, according to DuPage County prosecutors and Roselle police. Officials have said the alleged assault occurred in a minivan during the overnight hours after the party, and that the victim was taken to a hospital afterward. The defendants, all recent graduates, are charged with felony criminal sexual assault.
DuPage County State’s Attorney Robert Berlin and Roselle Police Chief Robert Barreto announced the charges Dec. 23, 2025, naming Kevin Niemiec of Prospect Heights, Zachary Mascolo of Arlington Heights and Jon Clary II of Bartlett. Prosecutors said Niemiec is charged with three counts of criminal sexual assault and was ordered held pending trial after a first appearance hearing, when Judge Joshua Dieden granted the state’s motion to detain him. Prosecutors said Mascolo is charged with two counts and Clary with three counts.
Dieden denied prosecutors’ detention requests for Mascolo and Clary, allowing their release while the case proceeds, officials said. The court ordered both men not to possess or consume alcohol and to have no contact with the alleged victim or her family, prosecutors said. The defendants are presumed innocent unless proven guilty beyond a reasonable doubt, and court conditions can be changed as a case develops.
Authorities said the Roselle Police Department was notified June 15, 2025, about a reported sexual assault that allegedly occurred at a Saint Viator High School graduation party the night before. Prosecutors allege that between June 14 and June 15, the three defendants sexually assaulted the victim inside a minivan. Officials said the victim later received medical care at a local hospital. Prosecutors have not identified the victim publicly.
Officials have not released detailed investigative records, but they described a months-long effort that included work by local detectives and county investigators. Barreto said Roselle police spent countless hours collecting evidence and working with prosecutors to bring the case to court. Berlin said the allegations are “extremely serious” and said he hopes the victim and her family receive the care they need to cope with what he called a horrific event.
The path from June to December involved multiple agencies, officials said, including the DuPage County Sheriff’s Office Digital Forensic Investigation Unit. While prosecutors have not outlined every step taken, the involvement of a digital forensics unit suggests investigators reviewed electronic material, such as phone records, messages or video, that can help establish timelines. Authorities have not said whether additional suspects are under investigation or whether more charges could follow.
Warrants issued Dec. 17 set in motion the arrests that brought the three men to court, prosecutors said. Mascolo was taken into custody Dec. 21 while driving near his home, according to prosecutors. Clary and Niemiec turned themselves in to the DuPage County Jail on Dec. 22, authorities said. The first appearances followed, leading to the judge’s decision to detain Niemiec and release Mascolo and Clary with conditions.
Cases like this often move through several early court stages, including hearings that set schedules, address evidence-sharing between attorneys and consider pretrial motions. Prosecutors have not said when, or whether, a grand jury could be involved, and no trial date was announced. Defense attorneys were not quoted in the initial public statements and it was not known what arguments they made at the detention hearings.
The school connected to the graduation party, Saint Viator High School, is based in Arlington Heights, while Roselle is in DuPage County. Officials did not say where the party was held beyond identifying it as a graduation party in Roselle, and they did not describe the number of attendees or whether any adults were present. The focus of the allegations, prosecutors said, is what happened in a minivan after the celebration.
Berlin credited investigators and prosecutors for bringing the case forward and singled out Assistant State’s Attorney Jaclyn McAndrew for work on the matter. Barreto said the department’s detectives showed persistence and professionalism and thanked county partners. Officials framed the announcement as a reminder of the seriousness of sexual assault allegations and the need for careful, thorough investigations.
The next court dates are already set. Prosecutors said Niemiec is scheduled to appear Jan. 12, 2026, before Judge Ann Celine O’Hallaren Walsh. Mascolo and Clary are scheduled to return Jan. 27, 2026, also before O’Hallaren Walsh. Those hearings are expected to help determine the pace of the case, including what motions may be filed and what evidence disputes may reach the judge.
For now, the case remains at the charging stage, with one defendant detained and two under release conditions. The next milestone will come in January, when judges and attorneys are expected to address scheduling and the next procedural steps as prosecutors prepare to present their evidence in court.
Author note: Last updated December 24, 2025.