Why were Italian and Israeli spies on fatal boat trip?

It reads like a pitch for a thriller. A group of tourists board a boat on a beautiful lake at the foot of the Alps. The boat capsizes in a sudden storm. Four drown as others swim to safety. In the days that follow, as authorities struggle to trace hotel bookings for the passengers, it emerges all were affiliated with the Italian and Israeli secret services.

- Angela Giuffrida ROME and Oliver Holmes

In the days since Gooduria, a 16-metre houseboat, was swallowed up by Lake Maggiore, there has been growing speculation over what its passengers were doing in this corner of northern Italy.

Last Thursday, a police source working on the investigation confirmed that eight of the boat's 21 passengers either currently or formerly served with Italy's secret service, and 13 had ties with Israel's.

Two of the victims - Claudio Alonzi, 62, and Tiziana Barnobi, 53 - had worked for the Italian intelligence authority. Another was a 50-year-old retired agent with Israel's Mossad spy agency. The fourth was Anya Bozhkova, originally from Russia, who was crewing the boat along with her Italian husband, Claudio Carminati, the boat's skipper. Carminati is being investigated over the deaths.

Carminati and Bozhkova ran a company called Love Lake and provided a "boat and breakfast" service on Gooduria, which only had a capacity for 15 passengers. The group boarded the boat, which was registered in the Netherlands, at the Piccaluga shipyard in Lisanza on the morning of Sunday 28 May for what was reported to have been a birthday celebration.