The death is believed to be a suicide, but Napa police are still investigating the case, Napa County sheriff's Capt. Tracey Stuart said.
An autopsy has been conducted, but toxicology tests are still under way. Stuart said the body did not appear to have suffered any trauma other than the burn wounds.
Lieberstein was identified using dental records, Stuart said.
Emergency personnel responded to a fire on a pedestrian and bicycle overpass of state Highway 29 south of Trancas Street at 4 a.m. Tuesday, Stuart said.
They found a man's burned body and pronounced him dead at the scene.
Investigators had trouble identifying the man and initially thought he was someone else but that possibility was ruled out Friday, Stuart said.
On Saturday, the Lieberstein family contacted the sheriff's office and said the deceased man might be their son, Stuart said.
The family had last heard from Adam on Monday night, the night before the body was found, Stuart said.
Gary Lieberstein and his wife Patti said there was no indication of a problem, Stuart said.
Adam Lieberstein lived in Napa but not with his parents, Stuart said.
"The Napa County Sheriff's Office wishes to express our deepest condolences to the Lieberstein family," Stuart said this morning.