Did the dealer commit the fraud, or were they merely an "innocent" victim? Your opportunities for remediation likely vary depending on the situation. At the very least, it appears the dealer was negligent in checking out the cars' title history - it was trivially easy for you to determine the fraud had occurred.
Odometer tampering is a federal crime. Perform a quick websearch - I found references to 15 USC 1984, 1988, 1990c. I believe treble damages are due - you can recover three times your losses.
Check with you state attorney generals' office. Most all have a consumer affairs division. See if they are able to assist you.
Decide what you want in terms of remediation. Does the dealer need to purchase the car back? Do you want a partial refund based upon the difference in value of a 120K mile car vs. a 60K mile car?
Don't let the dealer blow you off. They may stall, hoping you'll just go away - many people give up when they have been taken advantage of.