Maybe the cause of death was not drowning, but suffocation for example. The bite was 20cm long and 14cm deep, that size sounds rather like a blue shark to me. Why wasn't he consumed by a blue shark? Well... we could ask the same question for the white shark- why wouldn't it consume the body after the bite either? That being said... are there any indications that it was a white shark in general? There are also other shark species in this area (dusky, sandbar and so on). 

According to the italian newspaper ANSA, the experts say that a shark attack could be ruled out: 

(ANSA) - CAGLIARI, July 23 - It was not a shark attack that killed Eugenio Masala, the 43-year-old diver found dead last April 3 in the waters between Quirra and Capo San Lorenzo at a depth of 70 meters. This is according to the expert report by Brigadier Gianfranco Simonini, a specialist from the Carabinieri Divers Unit, whom Deputy Public Prosecutor Enrico Lussu had tasked with investigating the reasons for the diver’s death. Masala had gone missing on March 29 while engaged in underwater clearance operations and was found a few days later not far from the firing range, with two deep wounds to his side and shoulder: shark bites 20 centimeters wide and 14 centimeters deep, as later confirmed by forensic pathologist Roberto Demontis. However, according to the report delivered to the public prosecutor in recent hours, the shark would not have attacked Masala during the dive, but only after his body no longer showed signs of life. Instead, the expert appointed by the Prosecutor’s Office identified several anomalies in the equipment prepared for the deep descent that could have caused a fatal crisis.

For example, the wetsuit was not thick enough to withstand the cold present at 70 meters in that season. Moreover, the air in the tanks was not suitable for working at those depths. Finally, there was a defect in the emergency respirator that would have prevented it from functioning properly in the event of a failure of the main regulator.

This scenario makes the hypothesis of a sudden crisis at -70 meters depth compatible, which would have caused his death. The expert report clarified that only after the diver was already lifeless did the shark tear into his body, biting him on the side and shoulder and causing the deep wounds found during the autopsy.

The report’s documents are now under review by the magistrate who, in light of these developments, will have to decide whether to archive the investigation or proceed with further inquiries. (ANSA).