Celeste Rivas‘s body had been frozen, and as a result, it looks the L.A. County Medical Examiner will not be able to establish a cause of death … sources directly connected to the investigation tell TMZ.

According to those sources, the medical examiner received the body in horrendous condition … it was decapitated, and, while the torso was intact, the limbs had been removed and cut into multiple pieces.

We’re told all of the body parts were “partially frozen” … and had, apparently, been thawing out while sitting in the trunk of D4vd‘s Tesla.

Remember, D4vd’s vehicle had not been moved for several days when it was parked on a Hollywood Hills street near his rental home … which resulted in it getting towed, and then the body being found.

As TMZ reported, Celeste’s body was in such bad shape, initially, investigators did not know if it was male or female.

When the body was received by the M.E.’s Office, the initial determination was this was a victim of an “apparent homicide,” but our sources say the M.E. is now having trouble establishing an official manner or cause of death, and “It will most likely be ‘undetermined.'”

Other sources connected to the investigation tell TMZ the LAPD’s Robbery Homicide Division is viewing Celeste’s death as a homicide, and even if the official cause of death is undetermined, authorities can move forward with an arrest.

TMZ broke the story, D4vd is now considered a suspect in Celeste’s death. What’s more, TMZ has learned there is a second suspect who authorities believe helped D4vd in the dismemberment of Celeste’s body.

Mark Geragos appeared on the most recent “2 Angry Men” podcast and said he knows the name of the second suspect, and authorities have told him this person might have been involved “before, during, and after” Celeste’s death.

TMZ also broke the story … a critical part of the case involves a trip investigators say D4vd took to a remote area of Santa Barbara County in the middle of the night back in the spring, where he spent 2 hours.