For my story, at the scene of a crime, the police find shoeprints. Someone said I might have a plot hole, saying why didn't the police check records all around the city, for anyone who could have purchased those shoes within the last couple of years, when that style of shoes were being sold. But can the police do that legally? Can they check the sales records of every customer who could have bought those shoes, or does that violate some sort or rights to privacy laws? And even if they could do that, could the police be allowed to survey every one of those people who bought those shoes to see if any one of them is the perp?