Possible Clues:

• Deliberate extermination of a race of people
• The killing of a people on the basis of ethnicity or religion
• Nothing fits with information detectives last gave on killing
• Extermination of an ethnic group
• Racial murder
• No artist involved in stage direction of The Killing Fields, for one
• Surprise over denial from police department - it's a killer on a big scale
• Killing gone mad, countless initially die in torment
• Gene that has nothing to do with detectives is death for a lot of people
• Info on ordinary policemen's ultimate role in ethnic cleansing