The fiancee of slain Saudi journalist Jamal Khashoggi says she hopeful that his killers will be punished and has appealed to legislators in the European Union and the U.S. Congress to closely follow the case.

Speaking Friday at the launch of a book about the journalist, Hatice Cengiz also said she believes that Saudi King Salman "has a conscience" and will support Turkey's efforts to shed light on his killing.

Cengiz spoke a day after U.N. human rights expert Agnes Callamard said Saudi Arabia had undermined Turkey's efforts to investigate the death, which she described as a "brutal and premeditated killing."

Khashoggi, a Washington Post columnist who wrote critically about Saudi Crown Prince Mohammed bin Salman, was killed inside the Saudi Consulate in Istanbul on Oct. 2.