You sure? Nixon wasn't convicted of federal crimes, yet Ford pardoned him in 1974. Bush Sr. pardoned secretary of defense Casper Weinberger (who was not yet convicted) in 1992 (apprarently because the hearing against him next month may have revealed the crime of drug importation in the Iran-Contra affair....
I'm looking into that. I spoke to a lawyer friend tonight. Presidential pardons aren't his specialty but he said as far as he knew, a person who is pardoned either has to have been convicted or at least indicted of a crime in order to receive a pardon.
Here's what President Ford said:
"Now, therefore, I, Gerald R. Ford, President of the United States, pursuant to the pardon power conferred upon me by Article II, Section 2, of the Constitution, have granted and by these presents do grant a full, free, and absolute pardon unto Richard Nixon for all offenses against the United States which he, Richard Nixon, has committed or may have committed or taken part in during the period from July (January) 20, 1969 through August 9, 1974."
From the rest of Ford's text, it appears that this pardon was a preemptive pardon, made to
avoid a trial that was possibly to come.
Gerald Ford's Remarks on Signing the Nixon Pardon Proclamation
So, I stand corrected. In addition to convicted and indicted criminals, Presidents can pardon citizens who are facing
possible indictment but haven't actually been indicted.
However, I still don't think Ayers fits any of those categories. As far as I know, he's not facing an indictment for his crimes. Any attempt at a pardon now would only stir up indignation by his supporters against anyone implying Ayers had some wrong doing in his life that required pardoning.