Mary-Beth Tomaselli, left, and her sister, Linda Roberts, are accused of the 2015 murder of their father, which was initially thought to be a natural death. (Pinellas County Sheriff’s Office)

Their father was old and frail, ground down by his 85 years of life and hounded by cancer and dementia. He would die soon, his grown daughters Mary-Beth Tomaselli and Linda Roberts reasoned. They decided to help him make an early exit, police now say.

Anthony Tomaselli’s two children meticulously planned his death, authorities would later reveal. On the evening of March 6, 2015, Mary-Beth and Linda were at their father’s house, a whitewashed unit in a neighborhood of identical residences in Palm Harbor, Fla., about 25 miles northwest of Tampa. Mary-Beth’s adult daughter was also there. The sisters gave the younger woman sleeping pills so she would be oblivious to what came next.

Mary-Beth and Linda prepared their father an alcoholic drink spiked with more sleeping pills, police say, a concoction they hoped would quickly kill him. Anthony was sprawled on the couch, his breaths labored but still coming. Mary-Beth had put too much booze in the mixture, diluting the drugs. So Linda grabbed a pillow, smothering it over her father’s face. When he still failed to succumb, according to investigators, Linda stuffed a rag down Anthony’s throat and Mary-Beth pinched his nose and held down his squirming arms. He chest finally stopped heaving.

The next morning, the two sisters pretended to discover their father’s body on the couch. The paramedics at the scene assumed they were dealing with another elderly Floridian who had passed away overnight. Anthony’s death was listed as due to natural causes.

Mary-Beth and Linda had pulled off “the perfect murder,” Pinellas County Sheriff Bob Gualtieri told reporters at news conference Tuesday. But the sisters’ secret would eventually come out due to a bizarre love triangle.

As Gualtieri explained this week, both sisters began sexual relationships with the same man last fall. The unnamed individual learned about what truly had happened to Anthony four years earlier and brought the details to police.

On Tuesday, nearly four years to the day of Anthony’s death, Linda, 61, and Mary-Beth, 63, were arrested and charged with first-degree murder. According to a release from the sheriff’s office, the sisters both admitted to the charges in interviews with investigators. Court records indicate they have yet to enter pleas and do not yet have attorneys.

“This wasn’t even a cold case, because normally in cold cases we know that it's a murder, and either we know who did it and we just can’t prove it, or we don’t know who did it,” Gualtieri said on Tuesday. “In this case, it had all the appearances and signs of a natural death.”

The romance that finally pulled the curtain back on the murder started over drinks.

According to Gualtieri, last August or September, Mary-Beth met the man, who wasn’t identified, in a Pinellas County bar. “They developed a sexual relationship, and Mary-Beth subsequently introduced her sister Linda to this same male subject,” the sheriff told reporters.

Although she was married, Linda also began a sexual relationship with the individual, Gualtieri said. It is unclear whether the sisters knew they were both involved with the same lover.

Gualtieri said the man noticed “odd behavior” from Linda. “It was obvious to him that something was troubling her,” the sheriff said. After earning Linda’s trust, the man was invited to her home on Feb. 12. There, she confessed that her father had not died of natural causes in 2015. She and Mary-Beth had killed him.

“Because of Linda’s statements, the male subject took out his cellphone and began to videotape and audio tape Linda’s statements,” Gualtieri said.

According to the sheriff’s office release, Linda explained that the killing was “premeditated.” The sisters believed Anthony would die soon anyway, but he refused to go into an assisted living facility. Linda and Mary-Beth decided to “euthanize” Anthony due to his health and decision not to enter a facility.

The day after the startling confession, the man contacted law enforcement and handed over the recording. He began working with detectives, and during the next weeks, the man made additional recordings of statements from both Linda and Mary-Beth.

“This is all on tape,” Gualtieri told reporters.

In the later recordings, the sisters recounted the grisly details of Anthony’s death.

“They gave him the sleeping pills with the alcohol,” Gualtieri said. “That was their plan to kill him that way. When that didn’t work, they tried to suffocate him with a pillow. When that didn’t work, they stuck a rag down his throat, pinched his nose, and held his arms until he stopped breathing.”

Whatever intimacy or closeness existed between the man and the sisters, it seems to have made both women comfortable enough to dive deep in their memories, pulling out distinct details for him — and, thanks to the recordings, for investigators.

For example, Mary-Beth described how it had been “weird” after killing her father because a faint pulse still fluttered through his body after his death due to his pacemaker.

After killing their father, the women sold his house, they told the man, according to the sheriff. Linda and Mary-Beth split the $120,000 profit with their brother, who was not involved in the murder.

It is clear that had the women never fallen into the orbit of the same man, the truth about Anthony’s death may have remained hidden. The unidentified man — Two-timing Lothario? Conscientious citizen? — is the reason the case came to light.

“Oh yeah,” Gualtieri responded when asked Tuesday whether the sisters would have gotten away with the murder. “If they didn’t run their mouths and confess to this guy they met in a bar.”

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