Jamal Khashoggi probably thought the messages he was sending to fellow Saudi dissident Omar Abdulaziz were hidden, cloaked in WhatsApp security. In reality they were compromised -- along with the rest of Abdulaziz's phone, which had allegedly been infected by Pegasus, a powerful piece of malware designed to spy on its users.

Abdulaziz, as CNN reported last month, is suing the creators of Pegasus, Israel-based cyber company NSO Group, accusing them of violating international law by selling the software to oppressive regimes.

NSO has denied any involvement in the death of Khashoggi, insisting its software is "only for use fighting terrorism and crime."

The company was condemned as "the worst of the worst" by NSA whistleblower Edward Snowden during a video conference with an Israeli audience last November.

"The NSO Group in today's world, based on the evidence we have, they are the worst of the worst in selling these burglary tools that are being actively currently used to violate the human rights of dissidents, opposition figures, and activists," Snowden said.

The software, able to infect a phone after a single click on a link in a fake text message, then grants hackers complete access to the phone. Data stored on the phone, messages, phone calls and even GPS location data are visible, allowing hackers to see where someone is, who he or she is talking to, and about what.

In the case of Khashoggi, Citizen Lab researchers say the text message went to Abdulaziz, disguised as a shipping update about a package he had just ordered. The link, which Citizen Lab says it traced to a domain connected to Pegasus, led to Abdulaziz's phone becoming infected with the malware, giving hackers access to virtually his entire phone, including his daily conversations with Khashoggi.

In one text, before his death on October 2 at the Saudi consulate in Istanbul, Khashoggi learned that his conversations with Abdulaziz may have been intercepted. "God help us," he wrote. CNN was granted access to the correspondence between Khashoggi and Montreal-based activist Abdulaziz.

Two months later Khashoggi entered the building for what he thought was a routine appointment to pick up papers that would allow him to marry his Turkish fiancée, Hatice Cengiz. Minutes later, he was killed in what the Saudi attorney general later acknowledged was a premeditated murder.

The Saudis have presented shifting stories about Khashoggi's fate, initially denying any knowledge before arguing that a group of rogue operators, many of whom belong to Saudi Crown Prince Mohammed bin Salman's inner circle, were responsible for the journalist's death. (CNN)