Thesp Will Patton has signed on for the lead role in the Prufrock Pictures/Sagg Main Prods. co-production “Desert Saints.”The David Yudain produced pic is a thriller about a murder spree in the American Southwest. “Saints” will feature Patton as a highly educated assassin who terrorizes the region. “Saints” reps the debut of scripter-helmer Richard Greenberg. “Desert Saints” marks the first starring turn for Patton, who has previously appeared in supporting roles in such pics as “Inventing the Abbots,” “No Way Out” and “Copycat.” Production on “Desert Saints” will get under way in the fall. Patton is repped by Lisa Wong and Theresa Peters at William Morris.