The Black Light
I must've missed something. How did she know to take a black light downstairs and scan the walls. What made her think to do that.
She wanted the detective to send a forensics team but they couldn't because it wasn't technically a crime, so she decided to do some forensics of her own, presumably to see if it would pick up organic material such as blood.
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Never believe. Always question. Rebuke belief, a.k.a. bias, a.k.a. groupthink, a.k.a. ideology, the bane of skeptical, logical reason.