Shocking details of the "inhuman violence" suffered by an Italian student tortured and killed in Cairo began to emerge, as thousands of academics signed a protest letter demanding Egypt thoroughly investigates its worsening record of forced disappearances.

Giulio Regeni was found with both his ears chopped off, numerous broken bones and two missing nails that had been tore off from a finger and a toe, sources close to the investigation told Italy's Ansa news agency.

The body of The University of Cambridge PhD student was also covered in stab wounds, including some to the sole, consistent with an object similar to an ice pick. The revelations came after Italian forensics carried out a second autopsy when the 28-year-old's corpse was repatriated.

The analysis concluded Regeni died as a neck vertebra snapped due to a heavy blow or a violent twisting of the head. Italy's Interior Minister Angelino Alfano said the results indicate the student was exposed to "inhuman, animal-like" violence.

Italian media have unanimously pointed the finger at Egyptian security forces, arguing Regeni was probably arrested because of his ties to labour activists and tortured at length during a prolonged questioning.

The student had gone missing on 25 January, as Egypt marked the anniversary of the 2011 Arab Spring revolution that toppled Hosni Mubarak amid high security measures.The circumstance immediately sparked fears that the student, whose research focused on independent trade unions, had been caught up in a police swoop ahead of possible protests.

His half-clothed body was found on the side of a road on the outskirts of the capital more than a week later. Police initially dismissed the death as a road accident. Italy, which has sent an independent investigating team to Cairo, is maintaining pressure on the Egyptian government to conduct a transparent and comprehensive probe.

"We won't settle for purported truths," Foreign Minister Paolo Gentiloni told La Repubblica newspaper. "We want those who are really responsible to be found out, and be punished on the basis of law," the minister said.

The government of former general Abdel Fattah al-Sisi has so far dismissed all claims of security services involvement. "This is rejected. This is not the policy of the Egyptian security service," Interior Minister Magdy Abdel-Ghaffar told a press conference adding Regeni was never detained.

Nevertheless, more than 4,600 academics from all over the world have since signed an open letter calling for Egyptian authorities to look into their alleged widespread use of arbitrary arrests and violence, noting that "the Egyptian interior and defence ministries routinely practise the same kinds of torture that Giulio suffered against hundreds of Egyptian citizens each year".

"Those of us who knew of Giulio's disappearance before the discovery of his body were desperately concerned for his safety because he vanished in the midst of a security campaign that has resulted in mass arbitrary arrests, a dramatic increase in reports of torture within police stations, and other cases of disappearances," the letter published in The Guardian read.

Giulio Regeni Killed Cairo
Activists take part in a rally in memory of Italian student Giulio Regeni on 6 February outside of the Italian embassy in the Egyptian capital Cairo. MOHAMED EL-SHAHED/AFP/Getty Images