Every bone in Sweeney's face - except his left cheekbone - was fractured during the attack, Hood said. Almost all of the blows were struck when the teen was already lying on the ground, defenseless, Hood said.
"They were very heavy blows, and any one of them could ultimately cause death," Hood told the jurors.
Edward Batzig Jr., 18; Domenic Coia, 19; and his brother, Nicholas Coia, 18, showed no reactions to the detailed and graphic medical testimony.
The three are standing trial together as adults, charged with first-degree murder. If convicted, they face life in prison without parole.
Their alleged accomplice, Justina Morley, testified last week that Batzig struck Sweeney first with a hatchet. Domenic Coia attacked with a hammer, she said. And Nicholas Coia beat Sweeney with a rock, she said.
Also yesterday, Detective Carl Watkins told jurors that Domenic Coia admitted striking Sweeney with a hammer.
Domenic Coia said that before the group killed Sweeney, they listened to the Beatles song "Helter Skelter" dozens of times.
After Morley lured Sweeney to the vacant lot with the promise of sex, the three attacked.
"We just kept hitting him and hitting him. We took Sweeney's wallet and split up the money, and we partied beyond redemption," Watkins testified Domenic Coia said.
Afterward, the four engaged in a "group hug."
"It was like we were all happy [with] what we did," Watkins testified Domenic Coia said.
"Domenic, were you high on drugs during this beating of Jason Sweeney?" Watkins said he asked.
Watkins said the defendant replied: "No. I was as sober as I am now. It is sick, isn't it?"
The trial is scheduled to continue today before Common Pleas Court Judge Renee Cardwell Hughes. Closing arguments may begin during the afternoon.
Contact staff writer Jacqueline Soteropoulos at 215-854-4497 or firstname.lastname@example.org.