Hearings have ended in a disciplinary proceeding against a leading Martha’s Vineyard prosecutor who is under investigation for possible misconduct. But with numerous steps still ahead before the state Board of Bar Overseers, the matter could continue well into next year.

Final briefs are due early next month from attorneys on both sides in the case against Cape and Islands district attorney Laura Marshard, a West Tisbury resident. Ms. Marshard is being investigated by the BBO for possible misconduct in three separate criminal cases she handled in 2013 and 2014.

Formal investigations against prosecutors are considered rare.

The BBO is a 12-member board that takes action on complaints about misconduct by attorneys. A hearing before a three-person panel appointed by the board took place over eight days in May and June. The panel will ultimately make a recommendation to the board.

Documents on file in the BBO office in Boston include hundreds of pages of transcripts from the hearings, plus thick stacks of exhibits. Testimony covered a wide range from details of criminal cases and police investigations to the culture inside the Edgartown courthouse.

The cases at issue include a 2014 jury trial in Dukes County superior court for an assault case stemming from a brawl at an Oak Bluffs bar. During the trial, the judge took the unusual step of halting proceedings to admonish Ms. Marshard for misconduct after complaints from the defense attorneys.

Bar counsel also claims that in 2014 Ms. Marshard met with a defendant at the courthouse without his attorney present.

A third claim centers on a 2013 drug investigation, when Ms. Marshard allegedly failed to correct a state police sergeant who misrepresented a detail of an arrest before a grand jury.

In opening arguments, assistant bar counsel Stacey Best said in the three cases Ms. Marshard “exhibited a win-at-all-cost attitude” and violated the constitutional rights of the accused and failed to ensure justice, according to court transcripts.

But Ms. Marshard’s attorney Elizabeth Mulvey said Ms. Marshard had acted properly except in one instance — when she met with a witness in the 2014 jury trial with no one else present. Calling it a misstep, Ms. Mulvey said her client had admitted to the mistake and should not be disciplined for the action.

“She will be the very first prosecutor ever disciplined in Massachusetts for withholding evidence,” Ms. Mulvey said, according to the transcripts, adding that the action did not equate to a disciplinary violation.

She also noted that Ms. Marshard been assigned to the Edgartown courthouse in 2004 because district attorney Michael O’Keefe saw a need for a prosecutor who lived on the Island, and that she was in constant contact with the district attorney’s office.

“There is absolutely no evidence, no expert testimony, no testimony from any district attorney or any other lawyer that Laura Marshard should have done anything other than exactly what she did” in those cases, Ms. Mulvey said in her closing statement.

Earlier during hearings, Ms. Mulvey also argued that Ms. Marshard’s problems at the courthouse stem in part from a 2004 court case involving a relative of district court clerk-magistrate Liza Williamson.“Bad feelings remained, because on Martha’s Vineyard the summers end but the grudges linger on,” Ms. Mulvey said. She said tensions between Ms. Marshard and Ms. Williamson contributed the proceedings against the prosecutor.

Ms. Williamson testified over the objection of an attorney for the Massachusetts trial court who filed a motion in May to quash a subpoena ordering her to appear. Attorney Daniel Sullivan said at the time that Ms. Williamson had no additional information to supply in the case. The committee denied the request.

The committee also denied a request filed in June by Ms. Marshard’s attorney for an immediate finding on two of the counts, arguing that the committee had not had a chance to analyze and discuss the evidence and that it would be inconsistent with their role in submitting a recommendation to the board of bar overseers.

Other witnesses who testified included Vineyard defense attorneys and brothers Rob Moriarty and Tim Moriarty, state police Sgt. Jeffrey Stone, retired West Tisbury police chief Beth Toomey, and Oak Bluffs Sgt. Nicholas Curelli, as well as Mr. O’Keefe and other members of district attorney’s office.

Attorneys on both sides will further outline their arguments in proposed findings of facts and conclusions of law, due to the Board of Bar Overseers by August 4.

Potential outcomes in the matter range from dismissal to disciplinary action. The latter can range from a private warning to license suspension and disbarment.

Recommendations for license suspension or disbarment are heard by the state Supreme Judicial Court.