Fingernail marks on a 10-year-old Indiana boy's neck showed he tried to pry his teenage brother's arm loose as the older boy strangled him, a doctor testified during a Wednesday sentencing hearing.

Dr. Dean Hawley performed the autopsy on Conner Conley, whose brother, Andrew, pleaded guilty this week to murder in the boy's November death.

"There was a struggle, a violent struggle," Hawley, autopsy director at the Indiana University School of Medicine in Indianapolis, told an Ohio Circuit Court judge in the small Ohio River town of Rising Sun.

Andrew Conley, 18, faces 45 years to life in prison without parole. He can't face the death penalty because he was 17 at the time of the slaying. His sentencing hearing is expected to take three to four days.

Conley hung his head on his chest and folded his hands on his knees as prosecutors played audio of his questioning by detectives hours after he turned himself in to police.

"He kicked and threw punches and yelled for me to stop, but I couldn't," Conley said on the recording, the details of which police had released shortly after he was charged. "It just got out of control," he told detectives.

Conley said on the recording he didn't understand why he killed his little brother. He said he and Conner had not argued more than other brothers and he wasn't angry at the time.

"I just believe that I'm sick," he told detectives.

Conley said after Conner lost consciousness, he laid him on the floor and strangled him for about 20 minutes, at times taking breaks. "It was exhausting," he said on the audio.

He then taped a plastic bag over the boy's head to prevent blood from getting on the carpet, he said. Conley told detectives he dragged his brother's body downstairs and out to his car, put it in his trunk and drove to a local park where he dumped it.

Hawley said it was possible the boy was still alive when he was put in the trunk of the car, but that his injuries were too severe to survive. The doctor said he could not determine at exactly what point Conner died.

Defense attorney Gary Sorge questioned why police didn't read Conley his rights until after his brother's body was found, but Officer Wayne Siekman said even though Conley told them what he had done and where to find the body, they weren't sure at first that a crime really had been committed.

Sorge repeatedly objected to police testimony concerning details of the crime and other evidence as irrelevant because Conley already had confessed, but was overruled by the judge.

Conley told detectives he had thought about killing people since he was in eighth grade and identified with the TV serial killer Dexter. He said on the audio that he once tried to kill a cat with a knife, but couldn't go through with it.