Saudi Arabian Eid al-Sinani was sentenced to prison in 1997 and has remained there since because the ruling judge shifted absolute power to his father.
Sinanni was convicted of attacking his stepmother, according to the National Society for Human Rights.
Speaking to Reuters, Musab al-Zahrani stated: "We are optimistic that he will be released because he has been jailed for [almost] 16 years and there is no real charge.
"The son is left under [his father's] mercy."
In the Islamic legal justice system, law is not written and codified so rulings are subject to judges' opinion of Sharia law.
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