Considering what he decided for Carlo, Tessio, Frankie, Roth, and Fredo...Michael Corleone doesn't strike me as the type of guy who would allow Willie Cicci to walk off into the sunset.
Whether his testimony could be backed up or not.
Remember what he says to Tom... "I don't feel I need to wipe everybody out - just my enemies."
Apple
A wise and frugal government, which shall leave men free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned - this is the sum of good government.
