Gloves?
Okay, ever heard of gloves? The smart cookies even double glove. Nowadays, nitril is all the rage in the US.
With shows like CSI, juries are putting an unreasonable burden of proof on the prosecution for technical evidence. TV makes it look like a PM can be done in a day and DNA tests happen in a couple of hours. Most PMs take at least a week unless somebody REALLY rushes it. DNA tests can take up to a month or longer. And toxiology screening takes a minimum of 72 hours, assuming there's not a queue. AFIS can take as long as a week to run. But TV land solves crimes the same day.
This fingerprint chemical analysis will probably have very limited usefullness. But somebody will get creamed.