On a September afternoon in 2014, two men looking for ginseng in rural Tennessee came upon a grisly discovery: the skeletal remains of a young nursing student, Holly Bobo, who disappeared three years earlier when a mystery man, dressed in camouflage, accosted her outside her parents' home and led her away into the woods.
A total of six men were arrested for varying degrees of involvement in the case and three of them were charged in the kidnapping, rape and murder of 20-year-old Bobo — including Jason Autry, who earlier this month was offered federal immunity in exchange for his testimony against one of his co-defendants, according to court documents.
The offer means prosecutors are relying on Autry's testimony to convict Zachary Rye Adams, according to legal experts, who describe the case as "challenging" given the number of players involved and a potential lack of physical evidence.
"That means they need him desperately to convict the other guy," said David Raybin, a prominent criminal defense attorney and former prosecutor who helped write Tennessee code. "If they got an eyeball witness there, it makes for a better case."
"The bottom line is this: They've told him [Autry] that 'We won't prosecute you if you tell the truth,'" said Raybin, who is not involved in the case.
"You’re incriminating yourself but you get immunity from prosecution," Raybin told Fox News. "And usually under Tennessee law, if you are granted immunity and not prosecuted, that means you walk."
A spokesman for the Shelby County District Attorney's Office, which is prosecuting the case, would not confirm Friday whether federal immunity granted to Autry meant he would not be prosecuted on any of the charges. The spokesman deferred all inquiries to the office of the Circuit Court clerk in Hardin, Tennessee, which confirmed Autry had been granted immunity but said the documents did not say whether charges had been dropped or how prosecutors planned to proceed with the case.
Starting September 9, attorneys will select their 15 jurors to determine the fate of Adams, who has pleaded not guilty to kidnapping, rape and murder charges.
Prosecutors, meanwhile, are seeking the death penalty for charges of premeditated murder and perpetration of aggravated kidnapping and aggravated rape.
The trial was originally expected to begin this month, but was postponed until September after one of Adams' attorneys requested more time to test a gun believed to be connected to the death of Bobo.
According to court documents the gun, listed as an Arminius model HW5 .32-caliber revolver, was recovered in May and introduced as evidence by the prosecution. It was reportedly found underwater and court documents indicate it is believed to be the murder weapon.
Bobo, a nursing student at the University of Tennessee at Martin, who lived with her family in Decatur County, was last seen by her brother in the early morning of April 13, 2011.
Clint Bobo, then 25, reported seeing his sister being led by a man into the woods near their home at 7:30 a.m. Clint told investigators he initially assumed Holly was with her boyfriend, but said he grew concerned after finding blood outside, prompting him to call 911.
The Tennessee Bureau of Investigation then launched the costliest and most exhaustive missing persons search in the state's history, scouring woods and fields by air and foot. Authorities also used high-resolution underwater imaging to search lakes and ponds.
On Sept. 7, 2014, two men looking for ginseng found Bobo's remains about 400 yards into the woods north of County Corner Road in northern Decatur County, about 20 miles from her family's home.
Most of the arrests were made based on a confession by John Dylan Adams, who told investigators he saw his brother, Zachary Adams, and friend, Jason Autry, with Bobo at his brother's home after her abduction.
An affidavit states that John Dylan Adams "observed Holly Lynn Bobo sitting in a green chair in the living room wearing a pink T-shirt, with Jason Wayne Autry standing just a few feet away." Dylan Adams also told investigators that his brother was "wearing camouflage shorts" and said he told him "he had raped Bobo and videotaped it" — though the alleged videotape has not been found. John Dylan Adams since has claimed the confession was coerced.
Raybin as well as Tennessee attorney Rob McGuire note several legal challenges in the case.
"It’s a complicated case because you have multiple criminal actors involved," said McGuire, a criminal defense attorney and former prosecutor.
"There is limited physical proof because of the delay between the killing and the time the body was discovered," McGuire told Fox News.
Both Raybin and McGuire said: "The question is who did what and when and to whom?"
Despite hurdles, the attorneys expressed confidence that justice could be served for Bobo, the cousin of country singer Whitney Duncan, whom friends and family described as sweet and smart.
"There’s no one thing that you have to have in any case to convict of anything," said Raybin. "On the other hand, you have to have proof beyond a reasonable doubt."
"It can still be a strong case," added McGuire. "I do believe they can get convictions of people for the right crime and for the right reasons."
Cristina Corbin is a Fox News reporter based in New York. Follow her on Twitter @CristinaCorbin.