ISTANBUL — Turkey has concluded that Jamal Khashoggi, a prominent journalist from Saudi Arabia, was killed in the Saudi Consulate in Istanbul earlier this week by a Saudi team sent “specifically for the murder,” two people with knowledge of the probe said Saturday. Turkish investigators believe a 15-member team “came from Saudi Arabia. It was a preplanned murder,” said one of the people. Both spoke on the condition of anonymity to discuss the ongoing investigation. They offered no specific evidence to back up the account. Earlier Saturday, however, Turkey’s Anadolu news agency said the Istanbul public prosecutor’s office had opened...