Before their hanging, the men proclaimed their innocence and today historians believe many of the condemned men were falsely accused of murder. Before his hanging one of the man, thought to be Alexander Campbell, put his hand on the dirty floor of his cell and then placed it firmly on the wall proclaiming, " This handprint will remain as proof of my innocence." That handprint is visible today for everyone to view even though past wardens tried to eradicate it by washing it, painting it, and even taking down part of the wall and replastering it.
This article has more details:
In 1930, Sheriff Robert L. Bowman decided to put an end to the legend of the "hand on the wall." One night he brought the county road gang into the jail and had them tear out the wall that bore the bizarre shadow of a human hand. When the rubble was cleared, the workers put in a new wall and covered it with fresh plaster.
Sheriff Bowman, who supervised the work, retired for the night, confident that he had removed the "Irish miracle" forever. When he awoke and visited the cell the next day, he was shocked to see that the fresh plaster was marred by the vague outline of the hand. By evening, the palm of a hand was clearly visible on the cell wall.
In 1960, Sheriff Charles Neast, as was the custom up to that time, took up residence in the jail. To test the legend of the hand, he covered it with green latex paint. The shadow hand, however, re-emerged and became clearly visible again.
Ferdinand "Bull" Herman, a turnkey at the jail during the painting, observed the reappearance of the hand silhouette and liked to point it out to the many curious visitors to the jail.
Wikipedia claims (on the page of Alexander Campbell):
The handprint Campbell left is still there today, although the wall has been washed, painted over, and, according to some versions, even knocked down and replaced. A forensic scientist who examined the handprint with infrared photography in the 1990s concluded that it had never been painted over, and stated that the history of Campbell's execution suggests a right hand print on the wall, rather than the left hand print that is currently visible.
However, this is attributed to a 2007 Action News Special Report from ABC News via a broken link, so I can't find any further information about it.
Is there any evidence that this is a real "unremoveable handprint"? Are there documented attempts at painting over it or proof of the 1930's replacement of the wall? Alternatively, has anyone actually tried to disprove it, and if so, what happened?