The Transylvania County Sheriff's Office said that Clark Harman had been at Trails Carolina for less than 24 hours after he arrived in February from New York.
An autopsy report revealed the boy was smothered and suffocated. The medical examiner ruled the death as a homicide.
According to ABC affiliate WLOS, a press release from the DA said the investigation revealed that Harman's death was the result of suffocations, which, while tragic, did not involve criminal intent or recklessness sufficient to warrant criminal charges.
A counselor told detectives the boy had slept on the bunkhouse floor in a sleeping bag inside a bivy that had an alarm on its zipper triggered when someone tried to exit.
Trails Carolina described itself as a nature-based therapy program that helps 10 to 17-year-olds "work through behavioral or emotional difficulties."
The program had its license revoked by the state following the 12-year-old's death; the North Carolina Department of Health and Human Services found several violations. The state shut the camp down.
The property is now on the market for $3.2 million.
The Associated Press contributed to this report.