If they're going to arrest him, then it's grandstanding unless they can make the charges stick. The charge in this case is 'crimes against humanity'. This is the same sort of crime that the Nazi high officials were charged with during the Nuremberg trials. This is a charge that is associated with the highest form of evil known to history. While what has happened is reprehensible...it's not a crime against humanity. According to the ICC, who would be trying the case, the definition of crimes against humanity is:
"Particularly odious offences that constitute a serious attack on human dignity or grave humiliation or a degradation of one or more human beings. They are not isolated or sporadic events, but are part either of a government policy (although the perpetrators need not identify themselves with this policy) or of a wide practice of atrocities tolerated or condoned by a government or a de facto authority. Murder; extermination; torture; rape and political, racial, or religious persecution and other inhumane acts reach the threshold of crimes against humanity only if they are part of a widespread or systematic practice. Isolated inhumane acts of this nature may constitute grave infringements of human rights, or depending on the circumstances, war crimes, but may fall short of falling into the category of crimes under discussion."
So, unless the Pope/Vatican has been telling people to go ahead and molest children, it's not a crime against humanity. They have to be systematic, like what the Nazis did.