The following comes from a February 18 Canon Law Made Easy post:

Erwin Mena was a layman who somehow managed repeatedly to convince both clergy and parishioners of the Archdiocese of Los Angeles, California, that he was a bona-fide Catholic priest. After engaging in faux priestly ministry for some time, including celebrating Mass and administering the sacraments, it was established that he is nothing more than a con-artist, pretending to be a priest while stealing thousands of dollars from parishioners. Mena is now under arrest for grand theft, among other things.

How could this have happened? What should have happened in this case and didn’t?

Canon 903 explains how these situations are supposed to work. A priest who is not known to the rector of a church is to be permitted to celebrate Mass there, if (a) he presents a commendatory letter no more than one year old from his own superior, or (b) it can be prudently judged that he is not debarred from celebrating Mass. There are several different conditions mentioned here, so let’s examine this canon piece by piece.

First of all, if a visiting priest shows up at a church, and is already known to the pastor or other priest in charge, canon 903 does not even apply. If the priest in charge discovers that the visitor is his former seminary classmate, or recognizes him as a priest who is frequently seen on a Catholic television program, the visitor is “known” to be a priest.

So strictly speaking, there’s no particular reason under this canon to demand additional proof the man is a bona-fide priest. The priest in charge may, therefore, permit him to celebrate Mass immediately, with no conditions attached.

The situation is different, of course, if a visiting priest knocks on the door of a church and the priest in charge has absolutely no idea who he is. As canon 903 notes, a genuine priest should be able to present a “commendatory letter,” from his bishop (if he’s a diocesan priest) or his religious superior (if he’s a member of a religious institute). A sort of clerical ID-card also exists, traditionally known as a celebret, from the Latin word meaning “let him celebrate,” or “he may celebrate.” The letter or the celebret proves that the man claiming to be a priest is the real deal.

Now let’s see how all this applies to the strange situation of the priest-impersonator Erwin Mena, who deceived so many people in California. It appears that Mena had been identified as a fraud before, since his name was already included on a list distributed by the Los Angeles Archdiocese to all its clergy.

It would seem that at a minimum, priests of the Archdiocese are required to check the list when an unknown priest appears on the scene—and in this case somebody failed to do so. In January 2015, Mena showed up at St. Ignatius Church in L.A., when the pastor was going on vacation and needed a substitute—and by saying/doing all the things a real priest would say/do, Mena convinced not only the pastor, but the entire parish that he was a genuine priest—without ever providing a celebret or letter of suitability.

The Church is fortunate that very few priest-impersonators are such convincing liars as Erwin Mena appears to be! This tragic event has highlighted the need for priests worldwide to be careful about automatically assuming that a visiting priest is who he says he is. And if both canon law and (where applicable) local diocesan rules are followed, fake priests normally will be spotted and quickly stopped, before doing damage to the spiritual wellbeing of the faithful.