In 2019, Decker testified as an expert witness in a lawsuit against
Katy Perry, stating that Christian rapper
Flame produced a "unique" eight-note
ostinato — a repeating sequence of musical figures within a song — which Flame's legal team claimed Perry plagiarized. Decker further testified that the ostinatos used in Perry's 2013 song "Dark Horse" and Flame's 2008 song "Joyful Noise" share "five or six points of similarity." A jury verdict that found the Katy Perry song did infringe the copyright of Flame's song was overturned on appeal on the March 16, 2020. US District Court judge Christina A Snyder said "It is undisputed in this case" that the ostinato was "not a particularly unique or rare combination." Music theorist and YouTuber
Adam Neely criticized Decker's arguments as "intellectually dishonest", and claimed that Decker had "sold us all out" with his involvement in the case. ==Publications==