On Wednesday, Callamard joined Amazon.com Inc Chief Executive and Washington Post owner Jeff Bezos, as well as friends and supporters of Khashoggi and rights activists, who pledged to keep fighting for justice.
"We will never give up on this," said Andrew Gardner, Amnesty International's representative in Turkey, who condemned what he called "the sham trial".
He called for a U.N.-led investigation with the power to interview all suspects "whatever their level in government or position in power".
In the Riyadh trial, the suspects' lawyers have said they were duty-bound as state employees to follow orders, according to a June report by Callamard.
Two regional intelligence sources told Reuters previously that Qahtani oversaw Khashoggi's killing by giving orders via Skype to a team of security and intelligence operatives.
The CIA and some Western governments suspect Prince Mohammed, known as MbS, ordered the murder. In an interview with CBS program "60 Minutes" broadcast on Sunday, he denied that and called the killing a mistake, but said he ultimately bears responsibility as de facto leader.
Asked specifically about Qahtani and Asiri, he said: "...once charges are proven against someone, regardless of their rank, it will be taken to court, no exception made."
Qahtani's current location and activities are unknown.
Callamard has called for senior officials including MbS and Qahtani to be investigated, and said an international criminal probe should replace the Saudi trial, which Riyadh rejects. She said the crown prince's recent remarks are aimed at rehabilitating his image.
The Trump administration has pressed Riyadh to show "tangible progress" toward holding to account those behind the killing before the one-year mark, a senior administration official has said.
