ISTANBUL — Turkish investigators believe a well-known Saudi dissident was killed inside the Saudi consulate in Istanbul, five people involved in the investigation, or briefed on it, said on Saturday.

The critic of the Saudi government, Jamal Khashoggi, entered the consulate on Tuesday to obtain a document he needed to get married and never emerged, according to his fiancée, who had stayed outside.

Waiting for him inside the consulate, according to two people with knowledge of the investigation, were Saudi agents who had recently arrived in Turkey with the intent to silence Mr. Khashoggi. It was not clear if the plan had been to bring him back to Saudi Arabia alive, and something went wrong, or if the intention was to kill him there.

If confirmed, the killing could lead to an international scandal for Saudi Arabia and pose a daunting problem for Crown Prince Mohammed bin Salman, the kingdom’s 33-year-old day-to-day ruler, who has billed himself as a reformer committed to modernizing the kingdom.