Updated

A teenager charged with murder in the death of a 16-year-old boy in Alaska reportedly asked "What are you gonna do?" in the courtroom, in comments that may have been directed at the dead teenager's parents.

Walking out of the courtroom Tuesday, 16-year-old Bradley Renfro -- charged as an adult in the death of David Grunwald -- cocked his head back while passing Ben and Edie Grunwald in the front row, a reporter for the Alaska Dispatch News wrote.

"He said, 'What are you gonna do?'" private investigator Luke Smith told the newspaper, saying Renfro was looking at the Grunwalds. "And then he paused and looked at them again and said, 'Do something.'"

He also said the teen made a gesture with his hands indicating some kind of physical challenge.

However, Renfro's parents said he was actually talking to his father, who was sitting behind the Grunwalds. "He has no disrespect for the Grunwalds, I swear to God," the suspect's mother, Brittany Smith, told the newspaper.

Renfro was one of five teenagers charged as adults in the case. Erick Almandiger, Dominic Johnson and Austin Barrett also were charged with first- and second-degree murder, kidnapping and hindering prosecution. Eighteen-year-old Devin Peterson was charged with hindering prosecution and evidence tampering.

Each of the suspects pleaded not guilty in the courtroom in Palmer, KTVA reported. Almandinger was arrested Dec. 3 and the others were arrested Friday.

A criminal complaint against Almandinger claimed Grunwald was pistol-whipped by an acquaintance, driven to a remote location and shot.

Grunwald failed to return home after dropping off his girlfriend Nov. 13. His remains were found in a torched Ford Bronco north of Wasilla on Dec. 2.

Grunwald's mother said the girlfriend had mentioned a plan to stop at Almandiger's house on the night he disappeared -- although the mom said the family didn't know him.

Palmer is a 45-minute drive northeast of Anchorage.

The Associated Press contributed to this report.