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Norwell Woman to Serve Six Months in Jail for taping Grand Jury, Misleading Police Investigation into Murder

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Contact: Beth Stone (508) 584-8120

BROCKTON – A Norwell woman has pleaded guilty to charges she taped Grand Jury testimony and misled the State Police investigation into the murder of a Marshfield man, Plymouth County District Attorney Timothy J. Cruz has announced.

Brianne St. Peter McMahon (DOB: 07/30/79) of Norwell, pleaded guilty to three counts of Wiretapping, and one count each of Misleading a Police Investigation and Distribution of a Transcript or Distribution of Grand Jury Testimony with Intent to Interfere with Criminal Proceedings. Brockton Superior Court Judge Gary Nickerson sentenced McMahon to serve six months in the House of Corrections with three years of probation to run concurrent.

On September 16, 2015, 45-year-old Robert McKenna, was discovered dead in his home at 190 Damon’s Point Road in Marshfield. State Police and Marshfield Police worked around the clock to investigate the case and four people have been charged in connection with McKenna’s burglary/murder.

In October, 2015, St. Peter McMahon traveled with a friend who was also a witness to appear before the Grand Jury convened at Brockton Superior Court. While conducting Grand Jury, State Police assigned to the District Attorney’s Office learned that a phone may have been secreted into the Grand Jury in a witness’ jacket pocket and that phone was used to record the proceedings and interviews.

State Police seized the phone from the witness/friend and later that same afternoon, St. Peter McMahon came to the District Attorney’s Office in Brockton in an attempt to retrieve the lost phone. She was interviewed by State Police, charged and placed under arrest. Today’s indictments allege that St. Peter McMahon slipped her Samsung phone into the pocket of her unsuspecting acquaintance and taped the Grand Jury interview of that witness.

“One month after Mr. McKenna’s brutal, senseless murder, investigators and prosecutors were before the grand jury, presenting evidence and building a case against four people,” DA Cruz said. “The process of a Grand Jury investigation is one that is not public knowledge. This is to protect potential witnesses and foster a safe environment for witnesses to come forward to assist with investigations and help seek and obtain justice. Ms. St. Peter McMahon jeopardized that safety and security with her actions, and that disregard for the system is not to be tolerated or ignored.”

The case was prosecuted by Assistant District Attorney Amanda Fowle and was investigated by State Police Detectives assigned to the Plymouth County District Attorney’s Office and Marshfield Police.


December 19, 2017