According to this article, we can stop looking for Jack the Ripper:

A desperate McCain campaign has decided that unfounded accusations of 'Socialist' and 'Terrorist' aren't sensational enough to close the gap between McCain and Obama so they have decided to up the ante.

According to McCain campaign Operations Chief Steve Schmidt, McCain and Palin are getting ready to unveil a narrative that accuses Obama of being a time traveling Martian that made stops in 1880's London to commit crimes as 'Jack the Ripper'. In more modern times the 'Obama martian' is to be accused of chasing and attempting to murder the Warner Brothers cartoon hero Bugs Bunny.

The case is solved!