Defense lawyers took aim at a key prosecution witness in the Dewey & LeBoeuf criminal trial on Thursday, hoping to undermine three days of testimony that appeared to link the firm’s executives to the alleged accounting fraud at the heart of the case.

Under questioning earlier this week by New York County assistant district attorney Peirce Moser, former Dewey finance director Francis Canellas testified that he had implemented a series of accounting adjustments at the behest of former CFO Joel Sanders, former chairman Steven Davis and former executive director Stephen DiCarmine.