CNN) -- The grand jury in the case of Michael Brown's shooting didn't just face an onslaught of witnesses with conflicting memories of what happened the day white police officer Darren Wilson killed Brown, an unarmed black teenager. It also heard from witnesses who couldn't be believed at all. Some admitted lying. Others changed their stories under questioning. Prosecutors were so skeptical of one woman's account that they asked whether she might have dreamed about seeing the confrontation in Ferguson, Missouri, on August 9. Most of the dozens of witnesses who testified likely did their best to describe what they saw, but a review of thousands of pages of grand jury documents shows that untrustworthy testimony came from some witnesses on both sides.