The fall of Mamoru Samuragochi, the charismatic composer who now admits he hired someone to create his works, may have begun in October with a magazine article by Takeo Noguchi, a music critic and conductor.

At the time, Mr. Samuragochi was at the peak of his fame in his home country as "Japan's Beethoven," and his work was set to accompany skater Daisuke Takahashi at the Sochi Winter Games. But Mr. Noguchi thought he heard something out of tune in the Samuragochi persona, cultivated over more than a decade through...