Possible Clues:

• Artist's collection
• Case for governmental responsibility
• Extent of responsibility left one fool struggling
• Set of investments
• Power or oil frequently turned up in list of investments
• Left large-sized book in case
• Minister's responsibility to penetrate revolutionary turmoil of tropics
• Poirot disturbed about most of people in case
• Poirot mistaken about most of folk in case
• Art school submission