A New Hampshire jury has found Seth Mazzaglia guilty of first degree murder of the Oct. 9, 2012, death of Elizabeth ‘‘Lizzi’’ Marriott, 19, of Westborough, Massachusetts.

According to the Associated Press, the jury spent Thursday afternoon deliberating the fate of Mazzaglia, of Dover. The jury went home around 4 p.m.

Mazzaglia’s ex-girlfriend, Kathryn McDonough, swore under oath during the 19 days of testimony that she was present during the killing and that Marriott was “strangled” with a rope.

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McDonough, the prosecution’s key witness, also testified that she invited an unknowing Marriott to the home she shared with Mazzaglia to have a sexual escapade that included “bondage and discipline,” the AP reported.

After first telling authorities that Marriott died as a result of rough sex with Mazzaglia, McDonough backtracked and said Mazzaglia strangled and then raped Marriott.

The AP reported:

Mazzaglia sent her a text message at 10:26 p.m. asking, ‘‘We painting tonight?’’ — a coded reference to having sex with Marriott.

She replied: ‘‘Your decision, I guess. If you have a plan. Nervous.’’

‘‘I didn’t really know what he wanted to do,’’ McDonough testified.

Prosecutors said that Marriott willingly played a game of strip poker with Mazzaglia and McDonough, but refused two sexual advances from Mazzaglia, which allegedly spurred his fatal attack.

Marriott’s body has never been found after Mazzaglia and McDonough said they threw it into the Atlantic Ocean.

Friday’s verdict ensures that Mazzaglia will be sent to prison for life with no chance of parole. McDonough is currently serving up to 3 years in prison after pleading guilty to hindering prosecution.

Juror Maria Clifford said that she and her fellow jurors found McDonough to be credible despite the way she changed her story.

Bob Marriott, the father of Elizabeth Marriott, was relieved at the verdict, according to the AP.

‘‘The main thoughts were that she was a pathological liar most of her life and up until she took that witness stand, her life had been based upon lie after lie after lie,’’ said Clifford, 52. ‘‘I think Mr. Mazzaglia had control over her and she was afraid of him. We just thought, ‘She’s on the witness stand now and she doesn’t have anything left to lose,’ and she came to the realization that ‘I need to do the right thing.’’’

‘‘We will always miss her and we wonder what could have been,’’ Marriott said, his voice quavering. ‘‘In fact, the trial has been torturous for us. The truth of what happened to Lizzi is horrendous. And every time it’s been told, it has reinforced the despair that we feel.’’

He was also disappointed with the defense.

‘‘Blaming a victim who is unable to defend herself is a typical ploy used by defense teams. If you are dead, you cannot correct a mischaracterization,’’ he said.

New Hampshire Coalition Against Domestic and Sexual Violence expressed its condolences and sympathy to Marriott’s family.

Our thoughts are with the family and friends of Lizzie Marriott during this difficult time. We hope this verdict provides you peace. This trial showed us how extremely inhumane and selfish one person can be and we are grateful to the jurors for holding Lizzie’s killer accountable for his actions.