A security guard talks to a colleague at the entrance of Saudi Arabia's consulate in Istanbul on Oct. 26, 2018. (Lefteris Pitarakis/Associated Press)

Dan Nardello, a former federal prosecutor, is chief executive of the global investigations firm Nardello & Co.

The Saudi government has finally acknowledged that the killing of Post contributing columnist Jamal Khashoggi in its consulate in Istanbul was premeditated. But the regime’s earlier obfuscations suggest that a truly independent assessment of what happened in this appalling murder, and who was responsible, is unlikely. A rigorous, professional and impartial investigation is needed.

The firm that I lead has conducted an independent investigation in the Middle East; we know what a successful probe in that region looks like. In 2014, we began a 10-month investigation that confirmed allegations of abusive labor practices involving the thousands of migrant workers building New York University’s Abu Dhabi campus in the United Arab Emirates. Several steps are essential for an investigation into Khashoggi’s murder that will produce a report with legitimacy in the world’s eyes.

Appointing an independent entity with the requisite investigative skills, credibility and familiarity with the Middle East is crucial. The political agendas and entanglements of the Saudi royal family, Turkish President Recep Tayyip Erdogan and the Trump administration would cast suspicion on the objectivity of any investigation carried out by their governmental agencies. An independent, nongovernmental investigation conducted with the agreement of Saudi Arabia, Turkey and the United States would combine the benefits of credibility and the ability to operate free from the constraints imposed on government agencies by existing treaties.

Investigators should review all communications into and out of the consulate, starting with Khashoggi’s first visit on Sept. 28, when he requested the necessary documents to marry his Turkish fiancee, and continuing through his return visit on Oct. 2, when he was killed. During the first visit, he reportedly made an appointment to return and pick up the documents, which must have triggered communications leading to the dispatch of 15 Saudi agents to Istanbul, apparently with the intent of abducting or killing him. That entire communication trail is vital to determining who was involved and what roles they played.

A forensic study of all pertinent video and audio materials should be conducted to determine if they have been doctored. Turkey has leaked extensive information, but investigators need to see the materials and evaluate their authenticity. If that can be established, they will provide not only actual evidence about Khashoggi’s death but also valuable guidance when conducting interviews and open-source investigation of key players.

Confidential interviews need to be conducted with all of the Saudis known to have been involved in this matter — the consulate staff in Istanbul, the Saudi agents who were flown in and their superiors in Riyadh, Saudi Arabia. The interviews should be conducted outside the kingdom to minimize the potential for intimidation and compromised confidentiality. During our Abu Dhabi investigation, our interviews of migrant workers were conducted away from the job site for exactly that reason.

In particular, the 15-person Saudi team must be thoroughly investigated, through professional interviews and intense study of public information sources to determine exactly who they are, their jobs and reporting structures, and their networks of personal, family and professional relationships. The goal: gaining a clear picture of who these people are and who they really work for.

Getting to the bottom of this conspiracy will require locating Khashoggi’s remains or determining beyond any doubt how they were disposed of. Assuming the body can be found, the investigation must include independent forensic analysis of the remains and the site where they were discovered.

If the leaders of Saudi Arabia, Turkey and the United States can muster the political will to commit themselves to a fact-based investigation, there are proven methods available that will almost certainly reveal the truth.