Pietro Frenna died with a heavy heart and a head full of questions.

The 93-year-old’s death came before he achieved a years-long goal: to solve what family members consider the mystery of how his daughter ended up dead in the summer of 2008, her body floating about 100 miles from her Fort Lauderdale home.

“He always said, ‘I don’t want to close my eyes until I get justice for my daughter,’ ” Pietra Frenna quoted her father as saying.

The patriarch’s death in January was the family’s most significant loss since Josephine Frenna’s disappearance, which occurred during a bitter divorce.

“I’m praying night and day,” said Josephine Frenna’s mother, Anna, 87.

Anna Frenna and other relatives do not believe their loved one’s death was an accidental drowning, as authorities have ruled it.

“We want to get to the bottom of this, and we are not giving up. We can’t,” Pietra Frenna said. “We lost a brilliant diamond.”

The chief homicide prosecutor for the Broward State Attorney’s Office, Brian Cavanagh, said he understands the family’s exasperation.

“Evidence-wise, we are up the creek without a paddle,” he said. “It’s terribly frustrating; the circumstances upon which she drowned are inherently suspicious, but we have no proof.”

On the morning of Aug. 21, 2008, Josephine Frenna walked her son to his bus stop in front of their Galt Ocean Mile condominium. It was the last time Peter, then 13, saw his mother alive.

In a telephone conversation with her mother later that morning, Frenna, 51, said she was getting ready to meet her divorce attorney. She never made it to the 10 a.m. appointment.

The woman disappeared between the two events, investigators said. Her cellphone, purse, credit cards and keys were found inside the condo.

A beach bag containing various items, including the keys to Frenna’s condominium, was found in the sand. Pietra Frenna thinks her sister’s killer placed the bag there to make it look as if she went swimming.

Three days after she went missing, Josephine Frenna’s body was found in the Atlantic Ocean east of the Sebastian Inlet, about 12 miles north of Vero Beach, probably carried there by the Gulf Stream. The death was ruled an accidental drowning.

Family members disagree. They say Frenna was afraid of the water and would never swim alone, and they question why she would have gone to the beach less than two hours before a scheduled meeting with her attorney.

According to prosecutor Cavanagh, Frenna’s estranged husband, Gerardo DiMarco, and his son by another woman, Giovanni DiMarco, were initially considered persons of interest in the case. At the time of her death, Frenna had a restraining order against Gerardo DiMarco.

The order stemmed from a heated argument in July 2008 about keeping their residence under Josephine Frenna’s name. Gerardo DiMarco grabbed his wife and said, “I could take you right now and fling you off this balcony,” according to a State Attorney’s Office report.

Additionally, the report states that on the afternoon his stepmother was reported missing, Giovanni DiMarco told a relative, “Check the staircase or the beach — maybe she went swimming.”

Neither Gerardo nor Giovanni DiMarco could be reached for comment for this story despite repeated calls to listed telephone numbers.

The State Attorney’s Office began a review of the circumstances surrounding Frenna’s death in early 2009 after a family friend sent a letter to then-Gov. Charlie Crist.

An official memo dated May 18, 2011, recommended that the case be closed.

“The follow-up investigation confirmed that there was an articulable suspicion that Ms. Frenna may have actually been murdered and the circumstances possibly staged to look like an accidental drowning . . . possibly,” Cavanagh said. “But there was still not enough evidence.”

According to the report, Gerardo and Giovanni DiMarco’s cellphone records confirmed their alibis on the day Frenna disappeared, and their polygraph test results were inconclusive.

“There was nothing to connect anyone to her death,” Cavanagh said.

Pietra Frenna desperately hopes no one else in her tight-knit family will die with doubts about what really happened to Josephine Frenna.

“We hope someone will remember and come forward. As a family, we know as a fact she was murdered,” she said.

“We know that my sister will not come back, but we want justice.”