In U.N.H. murder case, why didn't witnesses call police?

DOVER, N.H. -- On May 27, 2014, Seth Mazzaglia went on trial for murdering Lizzi Marriott. Marriott was a 19-year-old college sophomore who had moved to New Hampshire to study marine biology--her life's passion. Thirty-three witnesses testified over the five week trial including two with a most unusual story to tell.

Days after the opening of the trial, Roberta Gerkin took the stand as a witness for the prosecution. Gerkin is a tarot card reader and was a friend, one-time sexual partner and spiritual confidant to Mazzaglia.

Watch: "48 Hours:" Dangerous Games

Gerkin's importance to the case was as an eyewitness to events on the night of Oct. 9, 2012, the night Lizzi Marriott died. But the question of why she and her boyfriend saw the disturbing scene she would describe for the court and didn't call police continues to haunt those close to the case.

Gerkin testified that she received a call from Mazzaglia's girlfriend, Kathryn McDonough, at about 10:50 that night, telling Gerkin that she and Mazzaglia needed help and asked Gerkin to come over to their apartment. Gerkin brought her boyfriend Paul Hickok with her, arriving about 20 minutes later.

Gerkin testified that as she walked in to Mazzaglia and McDonough's apartment she saw a young woman's body on the floor. Gerkin said she did not recognize the young woman and said she checked for a pulse but found none. Gerkin and Hickok both remember Mazzaglia saying "I've gone too far, I've gone too far," but said he did not provide any further explanation of what had happened.

On the witness stand, Gerkin said she and Hickok both urged Mazzaglia to call an ambulance and left the apartment believing he would call for help. In her testimony Gerkin said she wanted to give her friend the opportunity to do the right thing.

Gerkin and Hickok did not call police that night or in the days that followed.

In his statement, Mazzaglia told police that Lizzi had died in his and McDonough's apartment on Oct. 9, and explained that her body had been placed in the Piscataqua River in Portsmouth, N.H. --an area of notoriously strong tides and currents. Authorities immediately launched a lengthy and exhaustive search for Marriott's body, but no trace of Lizzi Marriott was ever found.

Rod Doherty, a longtime reporter and editor for the Foster's Daily Democrat, covered Mazzaglia's 2014 murder trial. Doherty told CBS News he was shocked the pair never called the authorities, saying, "I was fascinated by the lack of responsibility."

Doherty wrote a column about that choice during Mazzaglia's murder trial and says that column got a huge response from the community.

Despite moral outrage on behalf of many to Gerkin and Hickok's decision not to call for help, according to New Hampshire law there is no requirement to report a crime if you are a witness to it. Doherty added that "if either Gerkin or her boyfriend had agreed to do something that assisted Mazzaglia and McDonough in covering up the crime or otherwise helping them, they could be considered an accomplice and charged accordingly."

Neither Gerkin nor Hickok were ever charged with any crime relating to Lizzi Marriott's murder. Gerkin also agreed to cooperate with police through the fall and winter of 2012, creating a series of secret recordings with Mazzaglia's girlfriend Kat McDonough, to try and help police build their case for murder.

Kat McDonough pleaded guilty to charges of conspiracy, witness tampering and hindering prosecution, and was sentenced to three years in prison. Seth Mazzaglia was found guilty of two counts of first degree murder, including first degree premeditated murder, and first degree murder and rape, as well as two counts of conspiracy. He was sentenced to life without parole.

Because Lizzi Marriott's body was never recovered, her family has never had a formal funeral for her, and Lizzi Marriott has no grave.

At Mazzaglia's sentencing, Marriott's parents spoke of their desire to finally have a funeral for Lizzi now that the trial had concluded and her killer held accountable.

Sarah Prior and Lucas Cornfield contributed to this report. Prior produced the "48 Hours" investigation into the Marriott murder, "Dangerous Games." Cornfield was an associate producer on the hour. Watch the full investigation online.