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Defense lawyers challenge ex-girlfriend’s story at N.H. trial

Defense attorney Joachim Barth (right) questions Kathryn McDonough during the trial on Thursday.

John Huff/Foster's Daily Democrat/Associated Press

Defense attorney Joachim Barth (right) questions Kathryn McDonough during the trial on Thursday.

DOVER, N.H. — Lawyers for the man accused of killing a University of New Hampshire student spent most of Thursday cross-examining the prosecution’s star witness, suggesting that she hears voices that fight for control of her mind.

Kathryn McDonough had testified over two days that her former boyfriend, Seth Mazzaglia, strangled 19-year-old Elizabeth “Lizzi” Marriott of Westborough in October 2012 when Marriott refused to have sex with him. Mazzaglia has pleaded not guilty to first-degree murder charges.

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Joachim Barth, Mazzaglia’s lawyer, began his cross-examination of McDonough in Stafford County Superior Court by proposing that McDonough killed Marriott, not his client.

Barth reminded McDonough, 20, that when she was voluntarily interviewed the week after the murder, she accepted responsibility for causing Marriott’s death through the extended use of a bondage device.

“You described in detail that you were literally on her face for 10 to 15 minutes,” Barth said. “You described that she had a seizure and that she subsequently died.”

Barth said McDonough admitted in that interview with Barth and his investigators that Marriott was wearing a restraint that kept her from raising her head.

McDonough agreed that she changed her story after she accepted an immunity agreement, which prevents her from facing charges in Marriott’s death in exchange for her testimony.

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“You have since changed your account,” Barth said. McDonough is serving a 1½-to-three-year sentence for conspiracy, hindering prosecution, and witness tampering. She has admitted to helping dispose of Marriott’s body, which has not been recovered.

Barth spent most of the day questioning McDonough about her claim to have alternate personalities: different characters with names such as Scarlet and Charlotte that McDonough said she uses as a “coping mechanism.” She and Mazzaglia, who also adopted alternate personalities, spoke at length about their characters, according to Facebook messages presented in court.

Barth cited numerous texts and online messages in which McDonough detailed these personas to others. He quoted a recorded conversation between McDonough and a friend of Mazzaglia’s, Roberta Gerkin, in which McDonough said her memory of the murder was blocked by one such persona, Anay.

“What you’re talking about here is Anay trying to get control of [your] body,” Barth said, explaining the conversation to the jurors.

But McDonough testified that she was not controlled by the voices in her head the night of Marriott’s murder and that she lied about her memory being blocked by a persona.

“I knew what happened to Lizzi that night,” McDonough said. “I was aware, but I did not want to tell Roberta.”

Mazzaglia strongly believed that he had been a dragon in a past life, McDonough testified. Being around him, she said, strengthened some of her own supernatural beliefs.

“He seemed to take it so seriously that it felt like there was a good chance it could be true,” McDonough testified.

Barth suggested that rather than Mazzaglia controlling McDonough, it was Mazzaglia who went along with McDonough’s beliefs to further “a narrative you guys had going.”

During cross-examination, there were more than two dozen objections by the prosecution, many of them asserting that the defense was improperly characterizing McDonough’s testimony.

Earlier Thursday, McDonough concluded her testimony for the prosecution, once again telling jurors that Mazzaglia killed Marriott.

The jury was also shown a letter Mazzaglia wrote to McDonough in which he allegedly gave her instructions on how to answer police questions about their interaction with Marriott, in what prosecutors said was an attempt to make sure their stories were consistent.

The letter, sent from an incarcerated Mazzaglia and titled “Revised version of that night,” creates a timeline of events that, McDonough testified, was almost entirely false. The letter laid out a plan to frame Mazzaglia’s friend Paul Hickok.

McDonough testified Wednesday, in sometimes graphic detail, that she witnessed Mazzaglia raping and killing Marriott after Marriott rejected his sexual advances.

McDonough had lured Marriott, her co-worker, to the apartment with the promise of watching a movie or playing a video game. In reality, McDonough testified, she was offering Marriott as a sex partner for Mazzaglia, who was angry that McDonough had left him alone for 12 days.

McDonough, who broke down in sobs on the stand, said they folded Marriott’s lifeless body into a suitcase, took her to an island, and tossed her into the water.

Marriott’s father, Bob Marriott, who has been observing the trial from the front row, declined to comment Thursday.

Material from the Associated Press was used in this report. Claire McNeill can be reached at claire.mcneill@globe.com or on Twitter @clairemcneill.

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