Ankara (CNN) Saudi intelligence officer and former diplomat Maher Abdulaziz Mutreb played a "pivotal role" in the apparent assassination of Saudi journalist Jamal Khashoggi, a source familiar with the Turkish investigation has told CNN.

The source said that Mutreb was fully aware of "the plot" of the operation.

Mutreb, who was the first secretary at the Saudi embassy in London and has been described as a colonel in Saudi intelligence, is closely connected to Saudi Crown Prince Mohammed bin Salman. "He was seconded to an elite protection brigade within the Royal Guard to serve as the personal security force of [the crown prince]," a Saudi source told CNN.

Mutreb appeared in photographs alongside bin Salman during the crown prince's tour of the United States earlier this year.

Several US officials have told CNN that any operation involving members of the crown prince's inner circle could not have happened without his direct knowledge.

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