Colin Haag III, 20, stabbed 14-year-old Autumn Bartle at least 80 times, investigators say.
He was arraigned on Friday afternoon and is being held without bail. There has been no word on a motive for this shocking crime.
"Sometimes, as we stand here in this case, we look into the face of a killer, you don't get answers. You see only darkness," said District Attorney Matthew Weintraub.
Bartle died on Monday, three days after her mother came home to find her unconscious and bleeding on the living room floor.
Police say Haag lived in the home with Bartle and her parents.
Officers found "copious amounts of blood" in the bathroom, which also had evidence of a struggle. The district attorney's office noted that it appears Bartle tried to climb out of the window to escape but was unsuccessful.
Blood was also found on bedding and walls throughout the house, investigators say.
Haag was found walking with a backpack along State Road later that night, police say, and shot himself in the throat when officers approached. According to police, Haag said he shot himself because he didn't want to go to jail.
Inside the backpack was a notebook with blood matching Bartle's DNA, investigators say, and a blood-marked notation on the last page reading, "this is the last of Slim that's all you get it's the end 4 me."
Haag was treated and released for his gunshot wound. Haag was previously charged with stealing two handguns which had been reported stolen from the family home by Bartle's father.
After her death, Bartle's organs were donated.
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