The attack occurred in Upper Macungie, a township one hour northwest of Philadelphia. Martin said the woman died from "multiple" stab wounds, including defensive wounds on her hands from fighting off an attack.
After the killing, Martin said, Barnes and the juvenile went to a Walmart and bought alcohol, bleach and other items to clean up the scene. Martin said they buried the woman near a creek and attempted to hide a vehicle by pushing it into a pond.
Barnes and the girl met at a concert last October, Martin said. They attended an Eric Church concert in Wilkes-Barre with the woman this past weekend, he said.
Police in Upper Macungie say they discovered a suspicious vehicle with a large pool of blood inside. It was determined the car was actually in neighboring South Whitehall, so that township's officers were called to the scene.
When they arrived, the vehicle was gone. But officers noticed a mound of disturbed dirt on a snowy bank, under which they discovered the woman's body.
Officers found the suspicious vehicle partially submerged in a pond. It was registered to an Upper Macungie man with the same last name as the woman. When officers went to the owner's address, they say, they found the owner, Barnes and the girl.
All three were questioned, police say, and Barnes admitted stabbing the woman in the neck several times.
A man who appeared to be in his 40s answered the door of the large brick two-story, three-car-garage home Monday morning and directed all questions to attorney John Waldron.
"Please respect my family's privacy," he said and closed the door.
Waldron said he hoped to learn more about the charges.
"I grabbed a spotlight and I could see down across the road was a vehicle facing the wrong way," he said. "I seen all the blood in it. It was smeared on the passenger side window like there was a fight like there was a struggle. It was drops all on the dash on the seat … and all over the seat. And the car was locked. That's what scared me. I thought was I down here and [the suspect] was trying to get into the house."