https://apnews.com/0084c2f3927bffd5bcd82cd4e28d6afb > Anonymous sources in documentaries have often been reduced to a shadowy, voice-distorted figure — or worse, a pixelated blur. > But a new documentary premiering Tuesday on HBO has, with the aid of advanced digital technology, gone to greater lengths to preserve the secrecy of its sources while still conveying their humanity.