ROME (AP) — An Italian journalist who says he helped a former Vatican diplomat pen his bombshell allegation of sex abuse cover-up against Pope Francis says he persuaded the archbishop to go public after the U.S. church was thrown into turmoil by revelations in the Pennsylvania grand jury report.

Marco Tosatti said he helped Archbishop Carlo Maria Vigano write, rewrite and edit his 11-page testimony, saying the two sat side-by-side at a wooden table in Tosatti's living room for three hours on Aug. 22.

Tosatti, a leading Italian critic of Francis, told The Associated Press that Vigano had called...