The Istanbul prosecutor’s office said in a statement that Assiri and Qahtani were charged with “instigating the deliberate and monstrous killing, causing torment”.
Eighteen other suspects—including intelligence operative Maher Mutreb who frequently travelled with the crown prince on foreign tours, forensic expert Salah al-Tubaigy and Fahad al-Balawi, a member of the Saudi royal guard—were also charged with “deliberately and monstrously killing, causing torment”.
They face life in jail if convicted.
Mutreb, Tubaigy and Balawi had been among 11 on trial in Riyadh, during which sources said many of those accused defended themselves by saying they were carrying out Assiri’s orders, describing him as the operation’s “ringleader”.
The Turkish prosecutor said a trial in absentia would be opened against the 20 suspects but did not give a date.
The prosecutor had already issued arrest warrants for the suspects, who are not in Turkey.
Khashoggi, a Saudi insider-turned-critic, was strangled and his body cut into pieces by a 15-man Saudi squad inside the consulate, according to Turkish officials.
His remains have never been found.
The CIA, UN special envoy Agnes Callamard and Turkey have directly linked crown prince Mohammed to the killing, a charge the kingdom vehemently denies.