Choice D is the best answer. This question tests dash usage for dramatic revelation.

1. Context clues: There's a shocking revelation about who caused the fraud.
2. Meaning: A dash creates dramatic effect when revealing surprising information.
3. Verify: "The investigation revealed an unexpected truth—the company's own executives had orchestrated the fraud" is dramatic.

💡 Strategy: Use a dash for dramatic effect when revealing shocking or surprising information.

Choice A is incorrect because a comma creates a comma splice. Choice B is incorrect because a semicolon doesn't convey drama. Choice C is incorrect because while a colon works, a dash is more dramatic.