Lizzi was known as a hard-working student with a close group of friends and a strong bond with her parents, Bob and Melissa. Her friends described her as fun-loving, goofy, and lovable. To help pay her way through university, she worked at Target in Greenland and volunteered as a guide at the New England Aquarium in Boston, where she had been for four years. Her favourite exhibit was the touch tanks, and those who worked with her said she always greeted people with a massive smile.

Marine biology was Lizzi’s passion. In a college essay, she wrote: “I’ve always loved the ocean and its inhabitants. Someday, I’m determined to be a prominent figure when it comes to protecting our oceans.” Despite her busy schedule, she always made time for her girlfriend, Brittany Atwood, her first girlfriend. They had met in January 2012 and began dating in February. Brittany described Lizzi as beautiful, kind-hearted, caring, and trusting.

On October 9th, 2012, Lizzi texted Brittany from her night class, saying she was going to visit a friend’s apartment in Dover afterwards. She left a note for her aunt and uncle saying she’d be home around midnight. She never returned.

The next morning, Lizzi didn’t show up for her shift at Target. When Brittany called Lizzi’s parents expressing concern after receiving no response to her messages, the family realised something was terribly wrong. Lizzi was reported missing immediately. To vanish like this was completely out of character for someone who always kept everyone informed of her whereabouts.²

Investigators interviewed Kathryn McDonough, a friend Lizzi had recently met at Target. McDonough told them Lizzi was supposed to come to her apartment so they could take photographs at a local cemetery. She claimed that when Lizzi didn’t show up, she went to the cemetery alone.

The search intensified. Lizzi’s family travelled to New Hampshire, offering a $10,000 reward. The FBI joined the investigation. Cell phone records showed Lizzi’s phone was last used in Dover at 10:11PM. Her car was later found abandoned in a parking lot at the university in Durham, miles from where she was supposed to be.³

Two days into the search, investigators focused on Pierce Island in Portsmouth. The U.S. Coast Guard used sonar and underwater cameras to scan the murky waters of the Piscataqua River. Then came a shocking announcement: 29-year-old Seth Mazzaglia had been arrested and charged with second-degree murder. Though Lizzi’s body had not been found, investigators had determined she was dead.⁴

The arrest stunned those who knew Mazzaglia. He was a martial arts instructor with a black belt in karate and a University of New Hampshire graduate with a theatre degree. But even more shocking was his connection to Lizzi: Mazzaglia was the boyfriend of Kathryn McDonough, and they lived together in the very apartment Lizzi was heading to that night.⁵

A disturbing picture of Mazzaglia quickly emerged. He had profiles on dating and fetish websites under the username “DarkKaiser,” describing himself as dominant and sex-driven, seeking a submissive partner. A former girlfriend, Catherine Fish, revealed that Mazzaglia had strangled her during sex and became sexually abusive, throwing tantrums when she refused his advances.⁶

A neighbour reported hearing a woman’s blood-curdling scream from the apartment on the night Lizzi disappeared.

On Christmas Eve, Kathryn McDonough was also arrested. Prosecutors revealed that she and Mazzaglia had conspired to give investigators a fake alibi, claiming Lizzi never arrived at their apartment. McDonough had even sent text messages to Lizzi after her death, asking where she was, to throw off investigators.⁷

When their lies crumbled, Mazzaglia offered multiple versions of events before settling on a claim that Lizzi died accidentally during a consensual BDSM encounter. Prosecutors rejected this entirely, stating there was nothing consensual about what happened.

The investigation revealed a premeditated plot. Text messages showed that Mazzaglia had demanded McDonough bring him a friend to have sex with. He had written to her describing how he wanted to sexually dominate one of her friends while McDonough watched. Investigators believed the couple had been searching fetish websites for a sex slave and settled on Lizzi, McDonough’s new friend from work.⁸

When Lizzi was invited over, she thought she was coming to watch movies and play video games. The truth was far more sinister.

According to testimony later presented at trial, after playing strip poker, Mazzaglia propositioned Lizzi for sex. She refused. He then said she would watch him have sex with McDonough. Again, she refused. Enraged at being rejected in his own home, Mazzaglia put on gloves, crept up behind Lizzi as she sat on the sofa, and strangled her with a rope. He then raped her as McDonough watched.⁹

After Lizzi died, McDonough called friends Roberta Gerkin and Paul Hicock to help. When they arrived, they found Lizzi’s body on the floor with plastic bags over her head. Mazzaglia told them he had “blacked out” and said, “This time I went too far.”¹⁰

Mazzaglia led investigators to Pierce Island, where he had disposed of Lizzi’s body by throwing it into the Piscataqua River. The couple had then disposed of evidence in dumpsters, abandoned Lizzi’s car, and returned home around 6:15 AM. According to Mazzaglia, they then had sex because McDonough was excited about what had happened.¹¹

Investigators also discovered letters between the couple in which they conspired to kill Gerkin and Hicock, the only other witnesses, and flee to a country without extradition.

McDonough’s family claimed she had been manipulated by Mazzaglia. She had moved in with him at age 18 while he was 29, cutting off contact with her parents.

In July 2013, McDonough pleaded guilty to hindering prosecution, conspiracy, and witness tampering in exchange for testifying against Mazzaglia. Her sentence of one and a half to three years devastated Lizzi’s family, who called it a “gross injustice.” Lizzi’s mother told McDonough her actions were those of “a cold, calculating woman.” Her grandmother said simply, “You invited her to her death.”

The judge had strong words before McDonough was taken to prison: “But for you, Elizabeth Marriott would be alive today. But for your cowardly and selfish actions, she would be alive or this family would have a body to lay to rest.”

In May 2014, Mazzaglia’s murder trial began. The prosecution portrayed him as a sexually dominant predator who killed Lizzi because she rejected him. The defence tried to blame McDonough entirely, claiming she accidentally killed Lizzi during a rough sex act. McDonough testified for ten days, detailing Mazzaglia’s controlling behaviour and his demand that she bring him a friend to dominate.

After two and a half weeks of testimony, the jury found Seth Mazzaglia guilty of first-degree murder. At sentencing, Lizzi’s family delivered devastating victim impact statements. Her mother stared directly at Mazzaglia and said, “I want you to know that I unequivocally hate you. You are a cowardly, despicable person.”

Mazzaglia was sentenced to life in prison without parole. McDonough was granted parole in 2016.¹²

To honour Lizzi’s memory, her family established the Lizzi Marriott Intrepid Explorer Fund, a scholarship to help others pursue her dream of ocean conservation. Bob said her college essay about protecting the oceans made him smile and choke up, but more than that, it inspired him.

Lizzi’s body has never been found, robbing her family of the chance to say goodbye. With no body, there is no funeral and no gravestone to visit. When they want to speak to Lizzi, they go to Pierce Island and stare into the murky waters that flow out to the Atlantic Ocean.

As her father, Bob, once said: “I want to say goodbye to a person when they die. That is something I’ll never be able to do to my baby.”