I'm skittish about using the "smoking gun" analogy with reference to the Vatican's go-slow-on-abuse letter to the Irish bishops. Tucson's still in the rear view mirror and, besides, guns shouldn't smoke either.
But with all due respect to John Allen, his effort to reduce the significance of the Vatican's warning to a "public relations embarrassment" that doesn't rise to the level of a deadly weapon misses the point in my opinion.
The "1997 letter" as it will be exhibited in the court document doesn't itself carry the decisive load of guilt. It is, rather, this item adds to the cumulative stack of evidence of malfeasance.
As burden of proof grows, the efforts to explain the evidence as a misunderstanding of good intentions or as so historically conditioned that it would have made common sense at the time become even less credible. Ambiguity doesn't neutralize primary motivations.