Egyptian judiciary officials have refused to provide Italy with phone records of subscribers in a probe related to a slain Italian student, saying the request runs counter to the Egyptian constitution.

Senior prosecutor Mustafa Suleiman said on Saturday that Egypt rejected to hand over the phone records of mobile subscribers in the Cairo district, where Giulio Regeni, a doctoral student, resided before allegedly being tortured to death. The official said that was against the law and constitution of Egypt.

“This demand conflicts with and violates the Egyptian constitution, and would constitute a crime,” Suleiman said during a news conference, adding that the number of all subscribers in areas where Regeni lived, where he disappeared and where his body was found, could even reach a million.

Italy recalled its ambassador to Cairo on Friday to protest what it called lack of cooperation in the investigation.

Suleiman, who leads a senior judicial and security team investigating the issue, paid a visit to Rome earlier this week to review the controversial case with Italian officials. He said Italian investigators “conditioned further judicial cooperation on this demand,” which he said the Egyptian delegation to Rome flatly refused.

Regeni’s body was found on the outskirts of Cairo on February 3, nine days after he disappeared. His body bore signs of torture. The 28-year-old, who was a PhD student at Cambridge University, was reportedly conducting research on labor unions in Egypt.

There is the suspicion in Italy that elements in the Egyptian security services killed Regeni and that the student may have obtained sensitive information. Cairo has rejected such claims as baseless, saying a criminal gang carried out the murder.

Pressure has been high in Italy on Italian Prime Minister Matteo Renzi over the case.