Agnes Callamard, the special rapporteur for the U.N.'s Office of the High Commissioner for Human Rights, conducted a five-month investigation into Khashoggi's death last fall at the Saudi consulate in Istanbul.
The 101-page report into the October killing of Mr Khashoggi at the Saudi consulate in Istanbul lays out dozens of recommendations, including calling on United Nations bodies or Secretary-General Antonio Guterres to "demand" a follow-up criminal investigation.
In the months since Khashoggi's death, Saudi officials have exonerated the prince while the assassination has exonerated the crown prince, blaming rogue Saudi agents.
Prominent journalist and vocal Saudi critic Jamal Khashoggi, 59, was killed after entering the Saudi consulate in Istanbul last October.
Ms Callamard also determined that there was "credible evidence, warranting further investigation of high-level Saudi officials' individual liability, including the crown prince's", according to the report.
Senators unanimously passed the resolution in a direct rebuke to the Crown Prince and called for the Saudi Arabian government to "ensure appropriate accountability".
Khashoggi - who was never mentioned by name in the audio - was visiting the consulate to pick up papers to marry his Turkish fiancee, who waited for him outside the consulate before raising the alarm after he failed to emerge after several hours.
On top of the 101-page report's (pdf) conclusion that the Saudi kingdom is responsible for the killing, Callamard's findings also provided "chilling" new details of the final moments leading to Khashoggi's murder a year ago. His spokesman, Stephane Dujarric, said Guterres does not have the authority to do so without a mandate from an inter-governmental body.
Mutreb described Khashoggi as a "sacrificial animal", according to audio obtained by Callamard.More news: David Warner feared Australia career was over after ban
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Airing concerns about the Saudi judicial process, Callamard called for a suspension of the trial.
"Mr. Khashoggi's killing constituted an extrajudicial killing for which the State of the Kingdom of Saudi Arabia is responsible", Callamard's report said.
Callamard, an academic and rights advocate, noted limitations on her inquiry, which began in January.
Mutreb and 10 others are now standing trial in closed hearings in Saudi Arabia for their role in the crime.
The CIA has concluded that bin Salman very likely ordered the murder himself, based in part on the same understanding of his power over all actions taken by the Saudi security apparatus which Callamard referenced.
She also called on the United States to open an FBI investigation and pursue criminal prosecutions within the United States.
Saudi Crown Prince Mohammed bin Salman poses during a group picture ahead of Islamic Summit of the Organization of Islamic Cooperation in Mecca, Saudi Arabia, in June. USA officials say that, in an intercepted phone call, a member of the assassination team told one of the prince's aides to "tell your boss" that the mission had been accomplished.
These sanctions "fail to correspond to the gravity of the crime or to the fact that the state of Saudi Arabia is ultimately responsible for the violation of Mr. Khashoggi's right to life", she said.
"Failure to do so sends the message that journalists can be murdered with impunity".
Callamard said current sanctions do not go far enough and "fail to address the central questions of command and of senior leadership's responsibilities for and associated with the execution".