Eyewitness evidence is not generally accurate. We tend to think that eyewitenss evidence is the best possible evidence in a criminal proceeding. However, it appears that such accounts and identifications can actually be wrong a significant amount of the time.
For example, in this study, eyewitnesses performed in a fairly mediocre way. Those witnesses who had to make a quick decision as to which suspect was guilty picked the right one 67% of the time while those who were given time to think about it only managed 49% right. As another example, this paper discusses a number of studies that show that false memories or inaccurate memories can easily be introduced into an eyewitness's mind by a questioner.
Based on these sorts of studies, we should be rather skeptical about the value of eyewitness testimony. It appears that such testimony can very easily be inaccurate.