SEMINOLE COUNTY, Oklahoma - The body of a 41-year-old man from Thailand was found Sunday off Oklahoma state highway 56 near I-40, and OSBI special agents are searching for a key piece of evidence in their investigation. 

The Seminole County Sheriff's Office called in OSBI on July 23, 2017, to assist in the investigation after the body of Thanakrit Thuetong was found. Thuetong had lived in the United States since 2012, and he was last living in Florida, agents said. 

The medical examiner performed an autopsy, but doctors are waiting for toxicology results before determining the manner of death, OSBI agents said. 

Agents said surveillance video shows Thuetong inside a Seminole County convenience store the afternoon of Friday, July 21, with a black backpack. Agents learned during their investigation that he parked his 2009 black Pontiac G5 car in the parking lot of the store. But, in the video, Thuetong walks outside the store, past his car and along the highway. 

His body was found about a half-mile from the store but, the black backpack was not found, agents said. 

OSBI agents are asking whoever took the backpack to return it. Agents are only interested in the backpack, not the person who took it or why it was taken. 

Agents said Thuetong has relatives living in California, though they aren't immediate family. It is possible Thuetong was driving along Interstate 40 from Florida to California, agents said. OSBI agents are trying to get in touch with that relative.

If anyone has information on the backpack or on Thuetong’s death, call the OSBI hotline at 1-800-522-8017.