Megan Hargan is awaiting trial for allegedly killing her mother and sister in McLean, Va. But did she do it?

On the surface, Pamela Hargan and her daughters seemed to lead an enviable life.

Fueled by a desire to escape her small-town Illinois roots, as a young woman Pamela moved to the East Coast, quickly rising through the ranks of Lockheed Martin Aeronautics and becoming a top human resources executive there and later, at defense contractor SAIC.

A divorced single mom, Pamela traveled often for her demanding but well-paying job that enabled her to take her family on beach vacations and afford a $1.3 million house in the upscale Washington, D.C., suburb of McLean, Virginia.

Though she was eying retirement, at 63, Pam was no empty nester. Her oldest daughter, Megan Hargan, now 37, and Megan’s 7-year-old daughter, had been living with Pamela for several years, though Megan was married to a man in West Virginia.

“It was bizarre,” Pamela’s sister, Tamara North, 59, tells PEOPLE of the Megan’s long-distance marriage.

In the spring of 2017, Pamela’s youngest daughter, Helen Hargan, 23, moved back in with Pamela after graduating from Southern Methodist University in Dallas, Texas, while she waited for construction on a new home to be finished before starting grad school.

Megan was less than pleased. Over the years, “Megan had become very hateful,” says North. Not only did Megan and Pamela clash often, but “Megan hated Helen,” even though she and middle sister Ashley watched Helen when Pamela traveled for work, says North.

“It was an about-face; how could you hate the little sister you raised?” says North.

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Despite a seemingly happy public façade, behind closed doors, the relationship among the Hargan women had been “troubled” for some time, says North.

On one summer afternoon in 2017, North tells PEOPLE, “Something went very, very wrong.”

On July 14, 2017, police rushed to the Hargans’ home responding to a 911 call about a possible shooting. Inside, officers found Pamela’s blood-spattered body in her laundry room, dead of a gunshot wound to the head.

hargan crime scene
The home in McLean, Virginia, where Pamela and Helen Hargan were found shot to death.
| Credit: Tom RousseyWJLA-TV

Helen’s body was found in an upstairs bathroom, with a rifle muzzle resting on her abdomen and the butt between her feet.

What shocked North and others was that police said it was Helen who killed her mother before turning the rifle on herself.

“It was just so horrible,” says North. “But I knew right away that something was very wrong.”

Her instincts proved right, according to authorities. What initially appeared to be a tragic murder-suicide turned out to be a ruse to hide the unthinkable: a double murder, say officials in court records obtained by PEOPLE.

More than a year after the slayings, authorities announced they’d arrested Megan, who was charged on Nov. 9, 2018, with two counts of first-degree murder.

Megan Hargan, 37

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Police say otherwise. They allege that jealousy and greed led Megan to kill her mother and sister and stage it to look like a murder suicide. On the day of the murders and the day before, Megan allegedly tried to transfer money from her mother’s bank account, say police in an unsealed affidavit.

megan hargan
Megan Hargan being questioned by police.
| Credit: Fairfax County Police

Megan was allegedly using the money to buy a house, the documents state.

Pamela, says North, had bought Helen her new home, but said no to buying one for Megan.

Looking back, North says, “Never in a million years would I have dreamed that something like this would happen in my family. Never.”

“I just want justice for my sister and Helen.”