Maj. Quintanilla took over as Blue Book's leader in August 1963. He largely continued the debunking efforts, and it was under his direction that Blue Book received some of its sharpest criticism. UFO researcher Jerome Clark goes so far as to write that, by this time, Blue Book had "lost all credibility." Physicist and UFO researcher Dr. James E. McDonald once flatly declared that Quintanilla was "not competent from either a scientific or an investigative perspective." However, McDonald also stressed that Quintanilla "shouldn't be held accountable for it", as he was chosen for his position by a superior officer, and was following orders in directing Blue Book. Blue Book's explanations of UFO reports were not universally accepted, however, and critics — including some scientists — suggested that Project Blue Book was engaged in questionable research or, worse, perpetrating a cover-up. This criticism grew especially strong and widespread in the 1960s.