Carlos Rios, 24, was reported missing March 2.
Last month, police told ABC13 that someone who was going to buy the apartment at Club Creek near Woodfair was cleaning it when they smelled a strong odor. Neighbors in the complex had even noticed flies on the windows.
Investigators later discovered the body wrapped under a mattress.
The medical examiner said it is Rios' body, but has not concluded how he died.
Family members told ABC13 that Rios would visit a friend at that apartment often. That friend was Jesus Cardenas, the man who was identified as a person of interest in Rios' disappearance.
Investigators had searched Cardenas' apartment when Rios was reported missing. He was arrested and later released on a narcotics charge. Now he is nowhere to be found.
Investigators said there were signs of foul play in and outside the apartment.