The state can't prove — and his family may never know — who pulled the trigger, ending 16-year-old David Grunwald's life in November 2016.

While teen suspect Bradley Renfro's third and final interview with investigators didn't get them any closer to pinpointing who did, the lead investigator believes Renfro said enough about his role to implicate himself as an accomplice. 

An audio recording of the two and a half hour conversation is hard to understand at times, due to the quality of the file, but even the parts that are easy to hear are difficult for Grunwald's parents to listen to. 

Renfro tells troopers he watched as Grunwald was pistol-whipped. He describes the long drive searching for a place to murder Grunwald, the Palmer teen's desperate pleas for his life and the moment it ended. 

After a roadside conversation and then a formal interview with troopers, in which Renfro denied knowing anything about what happened to Grunwald, the third encounter came after troopers found Grunwald's body and arrested Erick Almandinger. 

In the beginning of the interview, Renfro tells troopers Almandinger's account of what happened — which had been revealed to the public through court documents — was true. Almandinger had pointed the finger at one of the other teens when asked who shot Grunwald. 

Minutes later, Renfro's story changed. He said Almandinger was actually the shooter. 

When asked what he said as the assault, kidnapping and killing happened, Renfro said, "Nothing, because I wasn’t trying to get beaten the f--- up like that too." 

Renfro's defense attorney has argued Renfro was compliant because he was scared that what happened to Grunwald might happen to him too. 

At one point during the interview, Renfro tells troopers he felt his life was in danger during the whole ordeal. 

Investigators couldn't get a satisfactory answer from him about when or how he knew Grunwald was going to be killed. Renfro told them he "just realized it" as Grunwald was asking to be dropped off at his girlfriend's house and pleading with them not to kill him. 

Alaska State Trooper Sgt. Tony Wegrzyn pointed to multiple statements made by Renfro during the interview that could indicate he was more involved than he wanted investigators to know. Renfro told troopers he offered suggestions to Almandinger about where they could go to commit the crime, helped escort Grunwald from the car, suggested a stop for gas cans to destroy Grunwald's Ford Bronco and even paid for the gas. 

Wegrzyn has also testified about how Renfro continued to spend time with the other three suspects after the murder and told troopers he wasn't scared of his friends because he took four years of taekwando. 

The state is expected to rest Thursday and the defense is set to begin Monday. 

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