ISTANBUL (Reuters) - Dozens of people gathered outside the Saudi consulate in Istanbul on Thursday in a vigil to demand “full justice” for journalist Jamal Khashoggi, killed after entering the building three weeks ago.

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Several carried cardboard images of his face and signs reading “Khashoggi’s friends”. One, his hands painted red, wore a mask depicting the face of Saudi Arabia’s de facto ruler Crown Prince Mohammed bin Salman.

Khashoggi, a Washington Post columnist and critic of the crown prince, disappeared after entering the consulate.

Saudi officials initially denied having anything to do with the disappearance, before changing that account to say an internal investigation suggested Khashoggi was accidentally killed in a botched operation to return him to the kingdom.

Saudi Arabia’s public prosecutor said on Thursday that the murder was premeditated.

“On this occasion, and from this place where the spirit of Jamal has been lost, we clearly state that we will not accept compromises in the case of his murder,” the group outside the consulate said in a statement, read out in Arabic, Turkish and English.

“We will continue to demand that all authorities across the Middle East immediately release all opinion leaders and political prisoners.”

The killing of Khashoggi has sparked global outrage and a crisis for the world’s top oil exporter and strategic ally of the West.

Turkey and Western allies of Riyadh have voiced deep scepticism about Saudi explanations of the killing.

U.S. President Donald Trump, the kingdom’s staunchest Western ally, was quoted by the Wall Street Journal as saying Prince Mohammed bore ultimate responsibility for the operation that led to Khashoggi’s death.

The people outside the consulate, some of whom had traveled from other countries for the vigil, lit candles in front of posters of Khashoggi.

One taking part was Yasin Aktay, an adviser to Turkish President Tayyip Erdogan and a friend of Khashoggi’s. He said the investigation should bring all those responsible to justice, “no matter where it reaches”.