LOL! Lots of rumors on the perfect crime circulate in prison/jail on how to get away evidence free.

Oil is what a fingerprint actually are.
There are many ways of lifting prints. Spraying something with oil after you touched it can eliminate some prints. WD-40 will actually make them permanent. WD-40 is mostly varnish.
Now in a liquid state when spaying, it can wash away the print, same as most soaps.

This also depends on the surface the print was left.

Wiping down what you touch can smudge prints to be un-readable.

Prints are interesting. On a piece of paper prints can be lifted a couple of hundred years later.

Prints are also a minor way to collect evidence.

Trace is left by everyone all the time where they have been. An example is dead skin cells. They contain DNA, better than a finger print. This is the same way a blood hound tracks someone or something. A lot of people watch TV shows like CSI and the like. Most departments don't have the resources and equipment that you see on TV. They are usually available only at a state level for special cases or a long wait for evidence tests.

If it were me, I wouldn't say a word to these ex-felons and just let them think they know best. That way if they do another crime, spaying everything down in wd-40 will make their case that much easier to prosecute. Statistics show that over 80% of felons will return to crime and return to jail.