While my personal view is that he's committed a crime totally unacceptable to the Catholic Church, namely, consential sex with an adult female, this is a rather interesting news release on the real reason.
Pope Benedict, Joseph Ratzinger, has scheduled a meeting with Italian President Giorgio Napolitano for Saturday, February 23 to discuss securing protection and immunity from prosecution from the Italian government, according to Italian media sources.
Ratzinger's meeting follows upon the apparent receipt by the Vatican of a diplomatic note from an undisclosed European government on February 4, stating its intention to issue an arrest warrant for Ratzinger, who resigned from his pontificate less than a week later.
http://itccs.org/2013/02/14/po ... apolitano-on-february-23/
This story has been doing the rounds for a while in both the alternate media and some christian media, it could be interesting to watch.