James Hughes was not reported missing until after his mother disappeared last week. Her body was found Monday near her home in Redditch, Worcestershire, and his in a suitcase in a garden shed.
Brian Kirby, Heather Wardle's partner, was released without charge Friday after two days of questioning.
"It is inconceivable that either Brian or Heather would hurt James," a friend told The Telegraph. "They loved him. Heather was so proud that she was his (care giver), that for 22 years she washed him, changed him, fed him, changed his nappies."
Hughes, 22, had a mental level of about 18 months and suffered from epilepsy. The friend said he might have died from a fall or an epileptic fit and that Wardle, blaming herself, decided to hide the body.
Paul Hughes, James's father, had become suspicious, friends said, because Wardle would not let him see his son.