Before he was cleared of criminal wrongdoing by the Justice Department on Friday, Sheriff Joe Arpaio liked to dismiss the investigation into him and his office as little more than a partisan witch hunt. But the very documents announcing the end of the probe undercut the sheriff's claims.

Arpaio has long argued that the probe began shortly after President Obama took office and was nothing more than a powerful Democrat targeting a lowly Republican sheriff...But Arpaio is wrong. The investigation has been going on longer than that. The case number assigned to the investigation proves it.

The number, USAO 2008-R09578...The letters at the beginning, USAO, stand for US Attorney's Office, where the case originated. The sequence of letters and numbers at the end, R09678, are uniquely assigned to distinguish one case from the next.

But the number in the middle, 2008, represents the year the case was opened. President Obama, of course, took office on Jan. 21, 2009.