ROME (AP) — Egypt's president has promised that investigators will work "night and day" to locate and prosecute those responsible for the torture and killing of an Italian student, insisting that the crime must not harm Egypt's financial and political relations with Italy.

President Abdel-Fattah el-Sissi made his first public comments on the case in an interview published Wednesday by the Italian daily La Repubblica and directed a message to the family of Giulio Regeni.

"I promise you that we will arrive at the truth, that we will work with Italian authorities to bring justice and punish the criminals who killed your son," he was quoted as saying.

Regeni went missing Jan. 25, the fifth anniversary of Egypt's 2011 uprising, when police were deployed across Cairo in a broad security sweep to prevent any demonstrations. His body was found nine days later bearing signs of torture.

Italian officials have repeatedly complained about a lack of transparency from Cairo amid media speculation that Regeni might have been a victim of the widespread torture and secret detentions by police that have been denounced by rights groups.

Egyptian officials deny any police involvement. La Repubblica said that during the course of the two-hour interview at the presidential palace, el-Sissi never once directly responded to questions about who might have been responsible.

Instead, he repeatedly referred to Egypt's fight against terrorism and its economic woes, and suggested that his opponents would have had an interest in harming Egypt's ties with Italy, its No. 1 trading partner in the European Union.

"There are many questions we have to ask about the circumstances of Regeni's death," el-Sissi said, noting that his body was found while an Italian business delegation was visiting Cairo and just months after Italy's Eni oil company announced it was developing a huge natural gas field off Egypt.

El-Sissi said specialized investigators are working "night and day to discover the true causes and reveal the circumstances behind this terrible death. We will not stop until we have reached the truth about Giulio Regeni's death."

Rome's chief prosecutor Giuseppe Pignatone visited Cairo on Monday to personally inquire about the probe, and el-Sissi said a delegation from the Cairo prosecutor's office would be in Rome in a few days to discuss improving coordination.

Italian news agency ANSA reported that at Pignatone's Monday meeting in Cairo, Egyptian authorities assured him that every possibility would be pursued in the investigation, even if that led it into areas that included law enforcement.

On Sunday, Justice Minister Ahmed el-Zind was fired, ostensibly over televised comments he made about the Prophet Muhammad that many deemed offensive.

In the same interview, however, el-Zind suggested that the perpetrators of Regeni's killing were known, prompting some commentators to speculate that he had suggested security services were involved and was fired for that.

"The crime is as it is known and circulated, and there's no need for us to repeat it," el-Zind said on private broadcaster Sada el-Balad. "I know and you know how the case is exactly," he added.

Pignatone told Corriere della Sera that the principle result of his mission to Cairo was that no more suggestions would be made about Regeni's character and that there was an agreement for having the "maximum collaboration" between the two prosecutors' offices. But he said the "signs of torture discovered are much more serious than those revealed during the first exam in Egypt. In fact, the same Egyptian colleague had to recognize that the crime was of a savage ferocity."

Aida Seif el-Dawla, a psychiatrist and co-founder of El Nadeem Center for Rehabilitation of Victims of Violence, said that Regeni's case bore all the hallmarks of police abduction and torture, such as the center sees on a regular basis and with increasing frequency.

"The cigarette burns, the marks from electric shocks, the fingernails pulled out, the dumping of the body — it's all very common in these cases," she said. Her center, which authorities ordered closed, is still partially operating but will not see patients until the close order is lifted.

"The phone keeps on ringing, the appointments are backing up," she said.

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Rohan reported from Cairo