Would like to see some serious evidence of this claim.
Lots of *incorruptables* around. On view, many.
Or did you mean this one in particular ?
In regard to Fr. Casey, maybe the Capuchins would supply you with further info.
In regard to the phenomenon in other cases, the following book may be of interest: "The Incorruptibles: A Study of Incorruption in the Bodies of Various Saints and Beati" by Joan Carroll Cruz
Apparently it is possible to view some of these "incorruptibles" at shrines and such, so you could go take a look for yourself.