Turkish authorities say prosecutors have found evidence that supports suspicions that missing Saudi journalist Jamal Khashoggi was killed inside Saudi Arabia‘s consulate in Istanbul.

A source at the Attorney General’s office, speaking on the condition of anonymity, said on Monday that Turkish officials had “found evidence that supports” their belief that the writer was killed, Al Jazeera’s Jamal Elshayyal reported.

“This is a significant step forward after several days of an impasse,” he said from Istanbul.

The report came hours after Turkish investigators entered the consulate for what officials called a joint inspection of the building where Khashoggi was last seen alive, entering the diplomatic post, nearly two weeks ago.

The source at the Attorney General’s office said their team also found evidence of “tampering”, Elshayyal reported.

Turkish officials say they believe Saudi agents killed and dismembered Khashoggi and say Turkey has audio and video recordings of it. Saudi Arabia has called the allegations “baseless” but has offered no evidence the writer left the consulate.

Meanwhile, CNN, citing two unnamed sources, said Saudi Arabia is preparing to admit that Khashoggi was killed as a result of an interrogation that went wrong.

The Saudis launched an internal investigation into the disappearance of Khashoggi earlier on Monday.

After speaking with Saudi Arabia’s King Salman, US President Donald Trump suggested that “rogue killers” could be responsible for the disappearance and presumed killing of the Saudi government critic.

Trump’s comments came after a 20-minute phone call with Salman in which Trump said the king adamantly denied any knowledge of what happened to Khashoggi.

Trump announced he had dispatched Secretary of State Mike Pompeo to the kingdom, to try and find out what happened to Khashoggi, a Saudi national who had been living and working in the US.

“The king firmly denied any knowledge of it,” Trump told reporters as he left the White House.

Trump said he didn’t “want to get into (Salman’s) mind,” but told reporters: “it sounded to me like maybe these could have been rogue killers. I mean, who knows? We’re going to try getting to the bottom of it very soon, but his was a flat denial.”

The US president gave no evidence to support the theory.

The comments marked a break from the Trump administration’s previous refusal to speculate over the fate of Khashoggi and came as the US president is under growing pressure to take action on the case.

Khashoggi is a contributor to The Washington Post and has written columns critical of Saudi Crown Prince Mohammed bin Salman.

The case has provoked an international outcry against Saudi Arabia, the world’s top oil exporter, with more media and business executives pulling out of a planned investment conference there this month.