The Suffolk DA’s office has dropped charges against a Dorchester man arrested by a Boston Police officer who reportedly violated department rules in a high-speed chase that killed three teenagers driving a suspected stolen car.

District Attorney Kevin Hayden has entered a nolle prosequi in Suffolk Superior Court against Joe Simmons Jr., dropping firearms charges that stemmed from a June 2023 traffic stop in Dorchester.

The dismissal of the case comes after the Boston Police Department concluded its more than year-long internal affairs investigation into Officer Triston Champagnie’s role in the January 2024 fatal high-speed pursuit that killed three teenagers on Dorchester’s Morrissey Boulevard.

In the nolle prosequi filed Tuesday, Assistant District Attorney Danielle Madden stated that a “necessary and essential witness” in the Simmons case is “unavailable and likely to remain unavailable.”

“Based on that witness’s unavailability,” Madden stated, “the Commonwealth cannot meet its burden to prove the charges beyond a reasonable doubt.”

BPD spokesperson Sgt. Det. John Boyle told the Herald later Tuesday that Champagnie, who earned $111,387.05 in total pay last year, is on paid administrative leave from the department.

A Herald records request for documents and findings from the internal affairs investigation into Champagnie’s misconduct allegations remains pending and is being processed, Boyle said.

An evidentiary hearing in the Simmons case scheduled for Wednesday and an October jury trial have been canceled, the case docket indicates.

Champagnie arrested Simmons months before the fatal chase, on June 20, 2023, on firearms charges, as the officer found a loaded Kel-Tec P-11 in the glove compartment of Simmons’ girlfriend’s SUV.

The traffic stop unfolded after Simmons allegedly drove through a red light in Dorchester and failed to use a turn signal.

Simmons’s defense attorney Zachary Cloud had taken exception to how critical parts of the traffic stop happened before Champagnie’s body camera was activated, which he said would have been a “key issue for the judge taking evidence in any motion to suppress hearing.”

ADA Madden had countered that Champagnie’s body camera captured “every portion of the interaction (except for) the reason for the stop.”

“Mr. Simmons is grateful that the prosecution finally decided to drop all charges against him,” Cloud told the Herald. “We always knew that Officer Champagnie’s arrest of my client was illegal. But sadly, this was part of a pattern of misconduct which began before our case and continued after, ultimately resulting in three teenagers needlessly losing their lives.”

Cloud had questioned Champaginie’s credibility and argued for the dismissal of his client’s case due to the drawn-out process, delayed by BPD’s refusal to comply with a court order to turn over records that the defense attorney had requested since last August.

Judge Katie Rayburn denied the dismissal request, finding “no egregious prosecutorial or police misconduct.” But she threatened to impose sanctions against BPD if it didn’t share internal affairs records and any misconduct complaints against Champagnie with Cloud by June 4.

In a motion to modify the Commonwealth’s protective order that blocked communication with his client about the BPD materials, Cloud made clear that the internal affairs investigation into Champagnie was damning.

“The Boston Police Department … has determined that the main officer in this case has been dishonest,” the defense attorney wrote in the motion filed with the court.

The records confirmed the validity of Cloud’s concerns over Champagnie’s behavior, the defense attorney told the Herald.

Per the Boston Globe, Champagnie, sitting in the passenger seat, and Officer Matthew Farley, the driver, continued to pursue a suspected stolen vehicle at a high speed despite Champagnie’s acknowledgment of a supervisor’s command to “terminate.”

Three teenagers in the car, which reached speeds of 106 mph, died after they crashed, while a fourth occupant survived. A pistol was found inside.

In the investigation, the BPD’s Bureau of Professional Standards found Champagnie had violated six department rules, including one that requires officers to be truthful in their reports, Cloud wrote in his motion earlier this month.

The five others included conduct unbecoming of an officer; failing to follow directives and orders; pursuit driving; pursuit driving – updates to operations; and failing to activate body-worn camera, according to Cloud’s motion.

The DA’s office did not press criminal charges against Champagnie and Farley, who were not allowed to have department-issued guns and uniforms as the internal affairs investigation played out.

A spokesperson for the Suffolk DA declined to comment about Champagnie on Tuesday.

Champagnie, who joined BPD after graduating from the Police Academy in November 2022, has faced numerous misconduct complaints, one stemming from a June 2023 incident, just days before Simmons’ arrest, with the officer “improperly handling a firearm,” causing it to discharge and damage property.

“Had he not received special treatment during his first instance of misconduct, this tragedy might never have occurred,” Cloud told the Herald. “We hope he is held accountable.”

Boston Police headquarters.