The John Gottis of this world are usually not regular churchgoers. They (and their victims) are often buried by the Church and they'll have their kids baptized by the Church and then married by the Church, but that's about it. You've watched too many movies. In parts of Sicily and Southern Italy the Mafia fights a running battle with the Church.
Add to this, the fact that in places like Italy, church-going is culturally more of a "woman thing" and not common among all men, still less Mafiosi, and you're left with a vanishingly small number of Mafia in the pews.
If you have have any information about Mafiosi tithing, I'm sure we'd all enjoy seeing it.
That aside, the "your bad guys are worse than our bad guys" line of schtick, is childish and lame. We can all point to miscreants who claimed affiliation to a particular religion until this thread stinks to high heaven.
It's also necessary to make a distinction between church policies/customs and the foul-ups of its members. It's one thing to empty the collection basket behind the Church's back and use the proceeds to buy a luxury yacht or condo and quite another for a Church to reward its pastors with material wealth which exceeds that of the most materialistic pagans.