"I've always wondered it. How can he be guilty if he had no free will?"
In Romans, Paul knows that the reader will ask this question.
Romans 9:19-22
"One of you will say to me: "Then why does God still blame us? For who [can] resist his will?
But who are you, O man, to talk back to God? "Shall what is formed say to him who formed it, 'Why did you make me like this?'"
Does not the potter have the right to make out of the same lump of clay some pottery for noble purposes and some for common use?
What if God, choosing to show his wrath and make his power known, bore with great patience the objects of his wrath--prepared for destruction?"
As for free will,
Adam and Eve had free will, we are sold to sin and when we are made dead to sin by the grace of God through Christ, we are slaves to Christ.
I don't see that we ever had free will.
Romasn 6:20 When you were slaves to sin, you were free from the control of righteousness.
Romans 6:6 For we know that our old self was crucified with him so that the body of sin might be done away with, that we should no longer be slaves to sin
Romans 6:22 But now that you have been set free from sin and have become slaves to God, the benefit you reap leads to holiness, and the result is eternal life
Peace