Complex sentence: Once both men had been placed in a position of safety, he returned to retrieve their Bren and proceeded to provide covering fire to the final stages of the assault, during which he killed four more Indonesians as they attempted to escape across the border.
Split into simpler sentences: Once both men had been placed in a position of safety, he returned to retrieve their Bren and provided covering fire to the final stages of the assault. Limbu killed four more Indonesians as they attempted to escape across the border.