Can’t they get DNA out of the leavings?
“Can’t they get DNA out of the leavings?”
They can. Will they? No.
The police are busy. They will direct their efforts to a combination of the easiest matters to resolve and the most urgent matters to address.
If a murder is involved, or a similar crime, such as kidnapping, counterfeiting, etc. the evidence gathered here might get used. But it would probably not even be used then to convict the criminal, just to identify and locate him, (her, it).
Other than that, justice will not be served unless it turns out to be low hanging fruit.