Well, Emma - I would suspect that the person was functioning as a lay volunteer member of a youth ministry team in 1988, and not as a priest. He committed his crimes between November of 1977 and May, 1978, and he ceased functioning as a priest in 1978.
Note the date the ex-priest was serving as a volunteer - 1988. Since about 2005, all but one Catholic diocese in the US has required the fingerprinting of all church employees, and of all volunteers who work with youth. I would hope this convicted criminal would not slip through the cracks nowadays, but it appears that he did - 22 years ago.

-Joe-

P.S. Emma and Mary Garvey are referring to the same case. It took me a little while to figure that out.