Now I’m not American but I did read something about this before but I’m quoting from memory… huge grains of salt to be taken with this.
Essentially I believe you can report it as “other income” not specify a source and refuse to elaborate if questioned or plead the 5th if it goes more serious. So in a way you are protected. They have to PROVE you got the money from committing a crime… “I’m just a lucky gambler”. Im pretty sure Whitey Bulger used to pay 30% more than a winning lottery ticket was worth to people so he could cash the ticket and justify his wealth.
I cant imagine the FBI are trawling tax returns, but if you hit their radar for some reason it will probably flag you as someone to be looked at. Just remember, tax evasion is how they got Al Capone but money laundering is also a crime so which one would you rather fuck with?
Talk to your employer about taking on the role on a “fixed term” basis of say 6 months. Tell them honestly why and see what they say. If you’re concerned about the lack in money see if you can take the 9 to 5 and supplement with the odd Sunday shift back on the floor to prop the wages up if that suits you.