The bodies of De Salis, who had worked in Tripoli for six years, and a woman from New Zealand were discovered by security forces near a gas and oil facility on Thursday.
The pair, described as close friends, were found on a beach near the coastal area of Mellitah.
De Salis is said to have been working as a power manager for First Engineering, bringing generators to Tripoli to provide electricity.
His family said they were shocked and devastated by his killing.
The UK Government has called on Libyan authorities to investigate the "murder" of De Salis and his female friend.