DOVER, N.H. — A man charged with raping and killing a University of New Hampshire student did not take the stand before his attorneys rested their case Tuesday.

Jurors will hear final arguments and judge’s instructions on the law Wednesday before deliberating the fate of Seth Mazzaglia.

Mazzaglia, 31, is charged with first-degree murder in the Oct. 9, 2012, death of 19-year-old Elizabeth “Lizzi” Marriott of Westborough, Massachusetts. Prosecutors say the Dover man strangled then raped Marriott after she rebuffed his sexual advances.

Robert Mitchell, the third and final defense witness, testified during cross-examination that Mazzaglia wrote him jailhouse letters saying he was catching up on episodes of the television documentary series “I Almost Got Away With It,” and reading books on abnormal psychology and interrogation techniques. Prosecutor Peter Hinckley asked Mitchell if he thought Mazzaglia might be plotting an insanity defense.

“It’s certainly possible,” Mitchell said.

In one letter Mazzaglia told Mitchell, “I will have a masterful understanding of the human psyche.”

During questioning from the defense, Mitchell described Mazzaglia as “both protective and belligerent” during an encounter with the family of Mazzaglia’s former girlfriend, Kathryn McDonough, when her relatives tried to convince her to move back home from the apartment the couple shared.

Mitchell, who said he used to play video games with Mazzaglia since they met during the summer before seventh grade, testified he moved to Franklin in August 2012 and did not see Mazzaglia in the months before Marriott died.

Jurors heard testimony over the course of 19 days since late May. McDonough, the state’s key witness, testified for 10 days.

McDonough initially told defense team investigator Lisa Greenwaldt — just days after Marriott was killed and Mazzaglia had been arrested — that Marriott died during rough sex with McDonough that involved restraints. She shifted the blame to Mazzaglia in her grand jury testimony in 2013, after being granted immunity from prosecution for any role in the killing.

McDonough said after Marriott was dead, she and Mazzaglia used Marriott’s car to transport her body to Portsmouth’s Peirce Island and threw it into a river that feeds into the ocean. It has not been found. They then drove the car back to the UNH campus and disposed of Marriott’s clothing and belongings in various trash bins.

Defense attorney Joachim Barth used his cross-examination of McDonough and defense witnesses to attempt to undermine McDonough’s credibility — which is seen as the linchpin in the case.

McDonough is serving a 1½- to 3-year sentence for hindering the prosecution, conspiracy and witness tampering. Barth in opening statements said McDonough sold her story to shave years off the punishment she faced.

Mazzaglia faces life in prison without possibility of parole if convicted of first-degree murder.

Defense lawyers unsuccessfully sought a mistrial on Tuesday, saying Hinckley in cross-examining Greenwaldt implied that her obligation to Mazzaglia transcended her obligation to the truth. The judge ruled that Barth had opened the door to that line of questioning during Greenwaldt’s direct testimony.

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