The 34-year-old Lincoln man was found on June 25 when a person passing by reported what they thought may be a dead body near the river just south of Beaver Crossing.
NSP says Nguyen was identified by his fingerprints, and from tips they received after releasing a photo of his tattoo.
Investigators say an autopsy shows Nguyen did not die of natural causes. Authorities aren't elaborating on what may have happened, but say they will continue to investigate his death as a homicide.
Anyone with more information should call the Statewide Crime Stoppers at 1-800-422-1494.