Years before the pivotal Battle of Yavin, specifically in 0 BBY according to the Years system, Lando Calrissian and his droid companion, L3-37, found themselves in a precarious situation. They were ambushed by an Imperial [interdictor] ship within the confines of the Halthor sector, an event that transpired while they were in the process of transporting a consignment of All Terrain Defense Turret walkers. The consequence of this surprise attack was the complete loss of the entire shipment for both Calrissian and L3.
Following the events of the Battle for Tatooine, the Tatooine rebel cell which was a part of the Rebel Alliance, obtained Lando Calrissian's holojournals, notably Holojournal Entry 1983712. They also intercepted communications from various criminal elements, hinting at the deployment of older, heavily-armed AT-DT walkers. Saponza came to the conclusion that someone had likely discovered Calrissian's lost shipment, and anticipated that others would be actively searching for the remaining cargo. Consequently, Saponza, along with his partner, initiated a mission to recover Lando Calrissian's shipment.