Turkish officials have said they believe he was killed-a claim Saudi Arabia has denied-with the controversy dealing a huge blow to the kingdom's image and efforts by its youthful crown prince to showcase a reform drive.
Horrendous screams were then heard by a witness downstairs, the source said.
"There was no attempt to interrogate him".
Salah Muhammad al-Tubaigy, who has been identified as the head of forensic evidence in the Saudi general security department, was one of the 15-member squad who arrived in Ankara earlier that day on a private jet. US officials have said this material supports the conclusion that Khashoggi was interrogated, tortured and then killed.
Various media sponsors of the Saudi conference have also pulled out, notably the UK's Financial Times and the American New York Times. Several pundits have suggested the "smartwatch recordings" were a cover story to explain why Turkey was so certain that the man had been killed by Saudi assassins.
The source told Al Jazeera that the murder took about seven minutes and said that Saudi forensics expert Saleh al-Tubaiqi dismembered Khashoggi's body and asked his colleagues to listen to music while he did it.
Pompeo's visit to Riyadh came hours after Turkish crime scene investigators finished an inspection of the Saudi consulate.
President Trump has previously said he does not want to halt a proposed $110 billion arms sale to Saudi Arabia - as some in Congress have suggested - because it would harm the USA economically.
"I think we have to find out what happened first", Trump told the Associated Press in an interview on Tuesday.
US President Trump said Tuesday he spoke with Saudi Crown Prince Mohammed bin Salman, who "denied any knowledge" of Khashoggi's whereabouts or fate. Trump also wrote that the crown prince "told me that he has already started, and will rapidly expand, a full and complete investigation into this matter".
There is as yet no official word from Turkey or Saudi Arabia, who are jointly investigating the Riyadh critic's disappearance, whether Khashoggi was actually murdered or killed by accident and whether Saudi Arabia was involved if his death is confirmed.
Khashoggi, 59, had been living in the US for a year in self-imposed exile and writing columns for the opinion section of The Washington Post.
Turkish President Tayyip Erdogan indicated that parts of the Saudi consulate in Istanbul had been repainted since Khashoggi's disappearance. The Saudi government didn't respond to a request for comment.
Earlier in the day, United Nations human rights chief Michelle Bachelet said the "inviolability or immunity" of people or premises granted under the 1963 Vienna Convention on Consular Relations "should be waived immediately".
Due to the seriousness of the case, the immunity generally accorded to diplomats "should be waived immediately", Michelle Bachelet said.