The son told Reuters on Monday that Mursi’s family did not know the location of his body and that their only contact with the authorities was through the family’s lawyers.
Mursi died on Monday at the age of 67.
He collapsed and died while attending a court hearing, Egyptian state media reported. He suffered a "sudden heart attack," state-run Ahram Gate said.
Egypt’s public prosecutor said there was no evidence of marks or injuries to his body but investigators would conduct a full autopsy and examine courthouse video for evidence.
Amnesty International urged a transparent probe into the circumstances of Mursi’s death, while other rights advocates seized on it as proof authorities were denying him proper medical care.