Possible Clues:

• Strange decay in the poison
• Very dangerous poison
• Poison in conspiracy an idea
• Something infiltrating democracy, an ideology that's poisonous
• Secrecy ultimately maintained, is able to 'arbour killer
• Some fancy an idea to give poison
• Cause of death in many a murder mystery
• A bit of bureaucracy -- an ideal cause of death?
• Dangerous substance that smells like bitter almonds
• Greenish-blue fish, it's poisonous