De Leon is the author of the note entitled "sniper nest location." The note informs Major Major Polanti at Camp Forlorn Hope that a small sniper's nest has been successfully set up near Cottonwood Cove as requested.
He includes details on supplies within the nest, bedding and miscellaneous items, but notes that there is no weaponry. Additionally, he states that the position is very close to the enemy camp and that after the sniper concludes their objective, they should quickly vacate the area.
David De Leon is mentioned only in Fallout: New Vegas.