Girlfriend in Marriott murder expected to plead guilty
Kathryn "Kat" McDonough, 19, of Portsmouth is expected to change her plea and be sentenced on July 25 in Rockingham County Superior Court as part of a deal struck with state prosecutors.
The anticipated guilty plea could signal that state prosecutors have turned McDonough into a key witness in the upcoming murder trial of her boyfriend, Seth Mazzaglia, who is charged with killing Marriott at his Dover apartment on Oct. 9.
Assistant Attorney General Peter Hinckley refused to comment on Marriott's scheduled plea hearing, or what effect it could have on the prosecution of Mazzaglia.
Marriott, a University of New Hampshire sophomore, was either strangled or suffocated to death on the night of Oct. 9, according to prosecutors.
Investigators spent months focusing along the Piscataqua River in Portsmouth and the edges of Peirce Island, where Mazzaglia claimed to have dumped Marriott's body.
"Our tendency was to believe that she was likely cooperating with authorities," Thompson said.
She remains free on bail. McDonough is accused of lying to police about her whereabouts on the night of the murder, and giving a fictional account of what she and Mazzaglia did on the day Marriott disappeared.
McDonough's lawyer, Andrew Cotrupi, could not be reached for comment on Monday.
During an interview in May, he remained circumspect about McDonough striking a plea deal with prosecutors, or whether she would become a state witness in her boyfriend's murder trial.
"She has nothing but regret to be involved in any way" in the events leading up to Marriott's death, he added.
"I think the evidence will be significantly different from the accounts some people have made," Cotrupi said.
State police were led to McDonough because of a single text message Marriott sent to a friend just hours before she was last seen.
Each of the charges against McDonough are Class B felonies, punishable by 3½ to seven years in state prison.