Answer:
A murder has been committed and there is no trace of the true killer. DNA proves that 7,472 people were present when the murder occurred... but is that true? Turns out the that the murderer killed the victim with a chemical substance, so no blood was present. The suspect also used vacuum dust from a hotel that contained 7,472 DNA's of other people, and one of them is the killer. Turns out to be that the killer used "cyanide" as a weapon of the victims death. But who is it?
Explanation:
