I guess it's unrealistic given how sensitive DNA tests have gotten, but I like to think cotton swabs come from a factory without human DNA on them.

That factory must have gotten a hefty lawsuit

The perfect cover and a deflection that cuts her boss where it hurts, too? That woman's a genius —though the serial murder'd make her a villain, sure.

Authorities used swabs not meant for collecting DNA and not guaranteed to be free if it. They basically saved money with the wrong item.

That's the problem with reading just a partial screenshot of an article that is much longer. This is the "consequences" section:

As a consequence of this severe case of contamination with human DNA in a series of forensic investigations, the International Organization for Standardization (ISO) published the standard ISO 18385 in 2016[8] to define the requirements for producing consumables free of human DNA contamination designated for collecting biological evidence at crime scenes: "Minimizing the risk of human DNA contamination in products used to collect, store and analyse biological material for forensic purposes".[9]

Ah, that makes more sense.