An eyewitness is still the best evidence. As I said before, there are numerous ways to impeach or discredit an eyewitness, but once you are confronted with an eyewitness you have an uphill battle to discredit them. They can be discredited by showing that the witness made a deal with the prosecution or they have a personal bias against the defendant. The reliability of an eyewitness is especially reliable in a case when they know the defendant. It's pretty hard to discredit them in that case.