The body was found by Nguyen Van Quy in a tank in his backyard on the night of Dec. 6 when he went looking for his dog.
He said the tank, which is in a large unfenced yard, has been unused for a long time.
The police conducted DNA tests on the body and said it was that of Nguyen Thu Thanh, a local woman who went missing in 2010 at the age of 22.
An autopsy also indicated she had been beaten before her death.
The police are investigating further.