Aiden is puzzled because the Port-a-Potty chemicals match the matter on Bill's jeans but those in his head wound. She breaks down the chemicals and focuses on the one that doesn't match: Dimethyl Benzyl Ammonium, which is used mostly in airplane toilets. Aiden puts it together: waste matter leaked out of a plane, froze in the atmosphere and came crashing down to earth, striking Bill Lamakkia on the head and killing him. Flack is nonplussed: "A crapsicle killed this guy?" he wonders.
It is an act of revenge, when you step on top of someone's car in freezing conditions when you have diarrhea, and crap all over the top of the person's car. The crap runs down the person's car, and freezes much like an ice-sicle over night. So when the person sees their car the next time, and sees brown 'ice-sicles' hanging from their car, they don't know you made diarrhea all over their car, which leaves you anonymous, and is a perfect act of revenge... Unless they go the FBI to analyze it.