The Pope's declaration, ostentatiously titled "Vos estis lux mundi" (you are the light of the world), will require an accessible and simple system for reporting abuse in every diocese. But, he said, "Where there is a difficulty, we must confront it, especially if a bishop is involved".
Kurt Martens, a professor of canon law of the Catholic University of America in Washington, DC, called the new rules an "immense and revolutionary gift to the entire Church".
Francis was then pressed by a German nun, who said the church must not rely exclusively on historic precedent for a future decision about female deacons, but on the needs of the church today. Every diocese will now be required to have a transparent reporting system.
"The crimes of sexual abuse offend Our Lord, cause physical, psychological and spiritual damage to the victims and harm the community of the faithful", the Pope writes in the letter.
The decree sets time limits for local investigations and the Vatican's response to them, and allows for retroactive reporting.
Cardinal Timothy Dolan, the archbishop of NY, lauded the reforms. Cover-up is defined as "actions or omissions meant to interfere with or avoid" civil or canonical investigations.
Bishops and other church superiors have been accountable only to the pope, and only a handfull have been sanctioned or removed from their positions. The pope finally defrocked McCarrick earlier this year after a church investigation determined he sexually abused minors and adult seminarians. Then the metropolitan has 90 days to conduct an initial investigation, subject to extension.
Maltese Archbishop Charles Scicluna, the Vatican's top sexual crimes investigator, told reporters the goal of that section was to mandate priests and nuns to report abuse within the church even in countries - including several in Latin America - where they are not obliged by civil law to do so.
The new law requires Vatican offices to share information throughout the process, since an untold number of cases have fallen through the cracks, thanks to the silo-like nature of the Holy See bureaucracy.
The reference to the Church's senior leaders is particularly significant as it includes bishops, who in many cases had been found guilty of covering up crimes reported to them. "A law without penalties is not a law at all - it's a suggestion", she added.
The guidelines, laid out in an experimental law, take effect on June 1 and will be re-examined following a three-year trial period.
The impact "likely will be felt most intensely outside the West, since places such as the US, Canada and some parts of Western Europe (though, ironically, not the pope's backyard in Italy), already have fairly robust reporting systems", said Vatican expert John Allen, on the online religious newspaper Crux Now.