The testimony of one person might be mistaken, and the testimony of two could be bought off, but with so many people on the scene, if you really wanted to bribe them all, just one unbribed witness would cause discrepancies in the testimony.
Everyone's testimony was consistent, which means that nobody was mistaken! Otherwise, the consequences are too dreadful to imagine... Someone meticulously schemed to bribe everyone in the marketplace!
Yet at that time, with people coming and going from the market, missing even one would lead to mistakes and give the game away, unless that person had a photographic memory to remember every face, and possessed immense power to track down detailed information on every single person entering and leaving the market to bribe them.
But even now, neither he nor Noah Bates could achieve such a feat.
With so many people passing through a market daily, the possibility of all being bribed simultaneously is virtually nil.