Marais said:SBI1,
Any time after you apply for I-485 with USCIS, your name will be sent to FBI to check with their database.
indoamerican said:RFE is Request for Evidence. This will be done onlye if USCIS need more information like medical, Pay / W2 or birth certificate or marriage certificate.
Whereas Fingerprinting is different it is done to verify you as an individual. FBI can be done anytime while your case is under process or review.
AOS /I485 is totally depending on the nature of the application, I am not sure whether you applied as EB1 /2 /3
I hope I answered your question.