How often did police join in the cover-up of sexual abuse?

Cardinal Sean Brady has apologized yet again for the failure to stop the predatory behavior of a pedophile priest, the late Brendan Smyth. If you’ve been following the story you know that Cardinal Brady—now retired, but once the Archbishop of Armagh, successor to St. Patrick, and Primate of All Ireland—became aware of Smyth’s misconduct in 1975, when he was a relatively young priest handling canonical affairs for the archdiocese.
He informed archdiocesan superiors about the abuse, but did not inform police. Smyth remained on the loose, a menace to children, until his arrest in 1994.

http://www.catholicculture.org/commentary/the-city-gates.cfm?id=1092