DOVER, N.H. (AP) — Lizzi Marriott left a message saying she'd be home by midnight.
Five weeks into her first semester at the University of New Hampshire, the sophomore planned to attend a Tuesday night lab class that would end at 9 p.m. She wouldn't have to hurry — she was staying with her aunt and uncle only about a half-hour drive from the campus where she'd transferred to study marine biology.
At 8:55 p.m., the 19-year-old sent a text saying she was going to visit a new friend, a co-worker at a department store near campus.
Less than two hours later, the former prom queen died with a rope around her neck.
The man charged with killing Marriott in October says her death was an accident during a night of consensual sex. Prosecutors call it murder. Either way, Marriott's body is gone — dumped in a river that pours into the Atlantic Ocean.
The circumstances of Elizabeth Marriott's death remain a dark mystery involving a couple who authorities say trolled fetish websites in search of sex slaves.
Thirty-year-old Seth Mazzaglio was a 2006 graduate of UNH with a degree in theater and a fourth-degree black belt in karate who taught at the dojo he started attending as a child in Kittery, Maine. Nineteen-year-old Kathryn McDonough is a former honors student who dropped out of high school in February of last year.
Authorities describe them as bondage enthusiasts who frequented fetish sites — him under the monikers "DarkKaiser" and "Enigmatic Shadows" and her as "Rouge Temptress."
The appeared together in a play — "Last Rites" — in July 2011 at a theater in Portsmouth. Eventually, they moved in together, sharing an apartment in Dover.
Police affidavits describe a text message Mazzaglia sent to McDonough in August. It described in lurid detail a bondage sexual encounter and suggested McDonough include a friend, someone to "offer" to him.
Authorities believe Marriott may have been that offering, lured to their apartment after class on Oct. 9 — not long after McDonough met her at work.
Marriott's disappearance set off a full-scale search in the seacoast region that is home to the UNH campus. But it didn't take long before Marriott's last text message — telling a friend she was going to "Kat's" — had investigators looking hard at McDonough and Mazzaglia.
Recently released court documents describe the couple's interviews with police starting three days after Marriott disappeared. First Mazzaglia said Marriott had never made it to their place that night — he had gone out for a run, hurt his ankle and was slow returning to the house. McDonough told police she went to a nearby cemetery in hopes of capturing images of ghosts with her digital camera.
But Mazzaglia's story soon began to change.
In an interview later the same day, he talked of bondage and sadomasochism. He implicated McDonough and another couple in harming Marriott, saying when he arrived home Marriott had a ligature mark around her neck. He suggested another man had done something terrible, but he wouldn't say what.
Finally, police said, Mazzaglia admitted he was involved. He and McDonough were playing strip poker with Marriott and that led to intercourse. Mazzaglia said he was having sex with Marriott — and tightening a rope around her neck — when she had a "seizure."
Mazzaglia told investigators neither he nor McDonough tried to revive Marriott or summon help. Instead, he told them, he put a grocery bag over her head and tied it at the neck.
A police affidavit describes interviews with another couple McDonough called the night Marriott died.
Roberta Gerkin said McDonough sounded "shaken" when she called asking Gerkin to come over at 10:49 p.m. When Gerkin and her housemate arrived, they both told police they saw a white female lying on the floor, a grocery bag tied over her head.
Gerkin told investigators when she used a box cutter to remove the bag, the woman's face was blue. Gerkin and her housemate told investigators they overheard the couple talking about "dumping the body."
Mazzaglia told investigators he and McDonough used Marriott's 2001 Mazda to take her body to Peirce Island in Portsmouth, where they threw it and her cellphone into the Piscataqua River. When Marriott's torso remained above water, he said, McDonough went into the water and pushed it under, making a joke about "Davy Jones' locker."
The pair then drove Marriott's car to UNH, left it in a student lot and discarded her belongings in trash bins, authorities allege.
Mazzaglia was arrested Oct. 13 — a day after he was interviewed — and McDonough on Christmas Eve. He is being held without bond, charged with first-degree murder. She has been indicted on charges of conspiracy and hindering prosecution. She was released on $35,000 bond on the condition she live with her parents in Portsmouth.
Trial dates haven't been set for either defendant.
Los Angeles Deputy District Attorney John Lewin, who has secured five first-degree murder convictions in all five "no-body" homicides he's tried, said such cases can sometimes give prosecutors greater latitude at trial to explore the character of the victim — showing how she wouldn't voluntarily leave family, friends and career behind.
While he would not discuss the Marriott case, he said defendants often convict themselves by giving multiple stories of what happened.
"You only have so much credibility," Lewin said. "You can't come in and argue five different things. But I want a jury to believe him because, when they find out half an hour later from his own mouth that he's a liar, it's three times as bad."
Attorneys for Mazzaglia and McDonough did not return calls seeking comment, nor did a lawyer for McDonough's parents.
Marriott's family has declined to discuss her death. Through a family spokesman, they have railed at that notion she died during consensual sex with Mazzaglia. Prosecutors say there was nothing consensual about Marriott's death but won't say what evidence they have to back up their contention.
Family members describe Marriott as "gullible" — someone who easily could be taken advantage of because of her trusting nature. One family friend from Westborough, Mass., where Marriott grew up, called her naive.
"She was just a good girl. That's probably what got her in trouble," Dawn Downey said. "She was too trusting and she was beautiful. Those two things will kill you."