A West Virginia woman killed five young children before setting her home on fire and fatally shooting herself in December, authorities announced Thursday. 

Fire crews in Williamsburg responded to a house fire just before 4 p.m on Dec. 8, Greenbrier County Sheriff Bruce Sloan said during a news conference. The body of Oreanna Myers, 25, was found next to a picnic table near the home.

A gun was recovered beside her and she had a gunshot wound to the head, authorities said. In the driveway of the home was a vehicle with three handwritten letters inside a ziplock bag. 

One of the letters was titled: "My Confession." 

"I had shot all boys in the head. I had set house on fire. I had shot myself in the head," the letter read, according to Sloan. "I’m sorry mental health is serious. I hope one day someone will help others like me. Mental health is not to joke about or to take lightly. When someone begs, pleads, cries out for help, please help them. You just might save a life or more lives. Thank you, O.A.M."

Greenbrier County Sheriff Bruce Sloan holds a press conference Thursday to give an update on a deadly shooting and fire that killed five children and one adult in December. A woman killed the children and set her home on fire before killing herself.

Greenbrier County Sheriff Bruce Sloan holds a press conference Thursday to give an update on a deadly shooting and fire that killed five children and one adult in December. A woman killed the children and set her home on fire before killing herself. (Greenbrier County Sheriff Department)

Authorities said Myers was the biological mother of three of the children -- ages four, three and one -- and stepmother to a seven and six-year-old.

In the days before the murders, she had sent the children's father several text messages exhibiting frustration that he was not staying in the family home during the week, Sloan said. 

The remains of the two of the children were discovered hours after first responders arrived at the house fire. At one point, investigators found another ziplock bag inside another vehicle with a letter to the children's' father. 

"I was not strong enough for you or this family," the letter read. "I'm sorry for my evil crime. I was not strong enough to fight these demons."

Myers diary, a cell phone and glass jar with a cloth with a spiral symbol on it were also found inside of the vehicle. The remains of the third and fourth child were discovered a short time later in the early morning hours of Dec. 9.

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The remains of the fifth child were found that afternoon, Sloan said. The family didn't have a history with Child Protective Services, he said. 

The West Virginia State Medical Examiner’s Office ruled the manner of the children's' deaths as a homicide.