Giulio Regeni, a postgraduate student at Britain's Cambridge University, disappeared in the Egyptian capital in January 2016. His body was found almost a week later, and a post-mortem examination showed he had been tortured before his death.
Italian prosecutors allege four Egyptian officials were involved in the killing but have been unable to track them down to issue summons. As a result, they are being tried in absentia.
Proceedings originally opened in October 2021, but were immediately suspended after the judge questioned whether the trial would be legitimate if it was not clear that the accused even knew they had been charged.
Italy's top court dismissed the concern last year, saying Egypt's failure to cooperate in locating the suspects should not stymie the trial. Prosecutors from both nations investigated the case but came to different conclusions.
Egypt said the killing was the work of criminal gangsters and denied any state involvement in Regeni's disappearance or death.
Italian prosecutors say Major Magdi Sharif, from Egypt's General Intelligence, Major General Tarek Sabir, the former head of state security, police Colonel Hisham Helmy and Colonel Ather Kamal, a former head of investigations in Cairo city, were responsible for the "aggravated kidnapping" of Regeni.
Sharif has also been accused of "conspiracy to commit aggravated murder."
The four men have never responded publicly to the accusations.
Regeni had been in Cairo to research Egypt's independent unions for his doctoral thesis. Associates say he was also interested in the long-standing domination of Egypt's economy by the state and military. Both subjects are sensitive in Egypt.
Prosecutors say they have evidence showing that Sharif got informants to follow Regeni and eventually had him arrested in a Cairo metro station.
The charge sheet says Sharif, and other, unidentified Egyptian officials, then tortured Regeni over several days, causing him "acute physical suffering."
When the trial initially opened in 2021, prosecutor Sergio Colaiocco told the court that Egypt had tried to sabotage the investigation and had prevented the suspects from being informed of the charges.
Colaiocco said Egyptian investigators had ignored 39 out of 64 requests for information, adding that the material that was handed over was often useless, such as video from the metro station where Regeni had disappeared.
The video was blank for the 20 minutes Regeni had been there, Colaiocco added.