With eyewitnesses, their account has to match evidence to see whose telling the truth or not. We have multiple eyewitness accounts, but little physical evidence to go on. It's not the eyewitness accounts that will cancel eachother out, but the layover of physical evidence and eyewitness accounts that will cancel out certain eyewitness accounts and bring others into focus as legit.
If eyewitness "A" has 75% of their account that can be proved or disproved by physical evidence then whether or not it is approved or disproved makes a pretty big difference in the legitimacy of the remaining 25% of their story. Where physical evidence is lacking that 25% part might be critical. If eyewitness B offers an account that simply can't be corroborated by physical it's hard to trust. If eyewitness C gives an account that can be matched 90% of physical and it does, the remaining 10% no matter what the 10% is weighted heavily. The investigators by this point should have a pretty good idea of the caliber of eyewitness accounts by this time.
We are stuck knowing little about physical evidence, but this will/should weed out legit eyewitness accounts from the forgeries. We can still play whack a mole with accounts that clearly don't match up known physical, but if known physical is very limited it leaves most eyewitness accounts somewhat murky. Judgement call on who would be more likely to lie/manipulate/embellish than others. Dorian Johnson should not have been paraded out on national TV, that account crowdfunds intent to create similar accounts. Poisoned the well IMO. Dorian is an interesting cat though, it appears that he returned the cigarellos to the clerk when Brown was in that store and took cigarellos. If this is true, speaks pretty heavy to positive of Dorians character (doing right thing in face of obstacles-in that case browns intent to steal cigarellos).