When Sandwich police officer Matthew Cotter was arrested Friday night on a drunk-driving charge after his car went through a resident’s bushes and into a parked car, he was eleven months into a deal. In September 2025 his department sustained a finding that he had been untruthful in an internal investigation, and instead of serving a five-day suspension he agreed to have it held in abeyance for one year, to be reduced to a written reprimand if he drew no further discipline. The year runs to September 15, 2026. The arrest was September 11.
That history is not from a leak. It is on page 224 of the POST Commission’s public list of sustained allegations against Massachusetts officers, a 1,094-page document the commission updates and posts on its website. Here is what it shows, what an abeyance agreement is, and what happens now.
The record
The commission’s list, updated March 11, 2026, shows four sustained internal-affairs matters against Cotter at the Sandwich Police Department, all listed under his certified status:
- November 2018. Conduct unbecoming an officer. Discipline: retraining.
- August 2024. “Inappropriate conduct by Officer Cotter discovered during the course of the original investigation.” Discipline: a suspension of one to five days.
- September 15, 2025, first matter. Conduct unbecoming: “unprofessional and discourteous with emergency medical personnel while involved in an off-duty incident.”
- September 15, 2025, second matter. Three sustained allegations. The first is classified under “Truthfulness or Professional Integrity”: “Det. Cotter was alleged to be untruthful after he reported he opened his window after it was banged on. Video evidence showed this account to not be true.” The second: he was ordered to stay away from a specific party and had contact with that party “despite being able to avoid it.” The third: insubordination, for violating “a clear directive to not have contact with members of this specific family.”
The discipline for both September 2025 matters is recorded identically: reassignment, and a five-day suspension for rule violations “held in abeyance for one year to be amended to a written reprimand if no further discipline during the defined period.”
The entries describe him as a detective. The department’s statement Friday called him an officer. Whether the reassignment took him out of the detective bureau is not stated.
What an abeyance agreement is
Police discipline in Massachusetts is negotiated more often than it is imposed. A chief who sustains a finding can suspend, but a suspension of more than five days for a civil-service officer can be appealed to the Civil Service Commission, and a union will typically grieve it. An abeyance agreement is the settlement: the officer accepts the finding and the sanction on paper, the sanction is not served, and if the officer stays out of trouble for a set period it is converted to something lesser. If the officer does not, the original sanction can be imposed on top of whatever the new matter draws.
The agreement is a probation without the word. It shifts the department’s leverage forward in time. An officer who signs one in September and is arrested the following September has, in the ordinary course, forfeited the deal, and the five-day suspension becomes the floor for whatever comes next, not the ceiling.
Why the untruthfulness finding matters more than the OUI
A drunk-driving charge is a criminal matter that will be resolved in Barnstable District Court, and a first-offense OUI in Massachusetts is commonly disposed of by a continuance without a finding and a 24D alcohol program. It is embarrassing for a department. It is not, by itself, career-ending.
A sustained finding of untruthfulness is different, and the commission’s classification of it under “Truthfulness or Professional Integrity” rather than “Other Misconduct” is deliberate. Since the POST Commission began operating in 2021, untruthfulness is among the findings that can support decertification, and it is the finding that prosecutors must disclose. A police officer with a sustained untruthfulness finding is a witness whose credibility the defense may attack in every case he testifies in, and the district attorney’s office is obliged under Brady and the Massachusetts rules to tell the defense the finding exists. The Cape and Islands District Attorney’s office will have had Cotter’s September 2025 finding on its disclosure list for a year. That is why the abeyance agreement included reassignment.
What happens now
Three processes run at once.
The criminal case. Cotter is charged with operating under the influence of liquor, negligent operation, a marked lanes violation and operating an unregistered vehicle. He is presumed innocent. Arraignment in Barnstable District Court has not been reported.
The department. He is on administrative leave. The department will open an internal investigation into the crash and, separately, into the relative who screamed obscenities at and allegedly shoved a news videographer at the scene. The department’s statement that its members “hold each other and themselves to the highest standards” is the language of a chief who expects to act.
The commission. Under chapter 6E, a department must report an officer’s arrest and any sustained finding to the POST Commission. The commission can suspend a certification while a felony charge is pending; an OUI is a misdemeanor. But the commission also reviews patterns, and an officer with a 2018 finding, a 2024 suspension, two September 2025 matters including untruthfulness, and a September 2026 arrest is a pattern. The commission’s decertification standard includes conduct that would disqualify a new applicant, and it has decertified officers for less.
Who is Matthew Cotter?
A Sandwich police officer, 44, arrested by State Police on September 11, 2026 on OUI and related charges after an off-duty crash on Grand Oak Road in Forestdale. He is on administrative leave.
What is his disciplinary record?
The POST Commission’s public list shows four sustained matters at Sandwich: retraining in 2018, a suspension in 2024, and two September 2025 findings including untruthfulness, resolved by a five-day suspension held in abeyance for one year.
What does “held in abeyance” mean?
The sanction is agreed but not served. If the officer draws no further discipline within the period, it is reduced to a written reprimand. If he does, the original sanction can be imposed in addition to any new discipline.
Can the POST Commission decertify him?
Decertification requires a commission proceeding. Untruthfulness findings and criminal convictions are among the grounds the commission considers. No proceeding has been announced.
Where can I look up a Massachusetts officer’s discipline?
The POST Commission posts a searchable list of sustained allegations and disciplinary actions by officer at mapostcommission.gov, updated periodically.
Has he been convicted of anything?
No. The OUI charge is pending and he is presumed innocent. The disciplinary findings are administrative, not criminal.
Disciplinary record from the POST Commission’s “Sustained Allegations and Disciplinary Actions by Officer” report, updated March 11, 2026, pages 224 and 225, read in full. Arrest facts from the Sandwich Police Department, Cape News, NBC Boston and WHDH, September 12, 2026. Matthew Cotter is presumed innocent of the criminal charges. General information about Massachusetts law, not legal advice.