Pamela Hargan, Megan Hargan and Helen Hargan.Photo: Fairfax County Police

Megan Hargan, with her mother, Pamela Hargan and sister, Helen Hargan

Tammy North couldn’t stop crying when she received the shocking news her that her older sister and niece were killed on July 14, 2017, in their $1.3 million McLean, Va., home in what police believed was a murder-suicide.

Then, on Nov. 9, 2018, the Illinois resident was floored when she learned that another niece, Megan Hargan, then 35, was arrested and charged with two counts of first-degree murder for allegedly killing the two women — and staging it to look like a murder-suicide, Fairfax County Police Major Ed O’Carroll said at a press conference at the time.

Now, three years after Megan’s arrest, she is about to stand trial for the deaths of her mother, Pamela Hargan, 63, a successful executive, and her younger sister, Helen Hargan, a 23-year-old recent graduate of Southern Methodist University in Texas.

On Monday, jury selection began for the trial, which is expected to last six weeks, theWashington Postreports.

Megan’s lawyer did not respond to PEOPLE’s request for comment but said in court records that Megan was not home at the time of the murders.

North tells PEOPLE she is still struggling with the deaths of her sister and niece and the fact that another niece is accused of killing them.

“I am overwhelmed at how hard this is to deal with,” North tells PEOPLE exclusively. “This is affecting me horribly. I feel sick every day.”

Her family’s tragedy began on a sultry July night in 2017, when police responded to a 911 call about a possible shooting at Pamela’s home.

Inside the immaculate colonial, Fairfax County police officers found Pamela shot in the head and lying in a pool of blood on the laundry room floor, according to authorities.

In an upstairs bathroom, they found Helen, also dead of a gunshot wound.

The muzzle of a rifle was found resting on her abdomen and the butt was between her feet.

Helen, police said at the time, had shot and killed her mother before turning the gun on herself.

“It was just so horrible,” Pamela’s sister, Tamara North, told PEOPLE previously.

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But jealousy and greed allegedly drove Megan, an unemployed single mom, to kill her mother and sister and staging it to make Helen look like she did it, say prosecutors.

The next afternoon, Megan allegedly stormed into the laundry room with a rifle and shot her mother in the head.

Minutes later, Megan allegedly headed back upstairs and shot her sister in the head.

Since North lives in Illinois and says she “doesn’t have the resources or mental strength to stay in Virginia for six weeks,” she won’t be able to attend the trial in person.

“I wish I could be there,” she says. “I want to know every detail. I want to understand.

“What transpired is killing me,” she says.

“The hardest thing for me is to wrap my head around Helen,” she says. “Her last moments must have been horrific.”

source: people.com