Circular reasoning is simply the logical flaw of begging the question...wherein one consciously or unconsciously has a conclusion and subtly uses that conclusion to justify and mold evidence to fit his view. Suspecting Ramsey family guilt is not an example. It is also not circular reasoning to believe them innocent. Reasoning becomes circular when conclusions serve to alter perceptions of realities of evidence. Most of the thoughts here seem derived from evidence and are entitled to respect. The notion that mostly circular reasoning makes people suspicious of the Ramseys is false, irrational, and illogical. And to assume one is the sole proprietor of the final answer on a currently unknowable matter is also not rational.
But there are in fact certain comments expressed here that are an example of circular reasoning...one in particular is a campaign to proselytize the possibity of an intruder. Whether it started by assuming the family innocent as mandating an intruder, or vice versa, I have seen it to the point of clearly affecting the view of evidence. In some case contrary evidence is ignored and in others, things claimed to be supporting evidence that are not. The fact is that belief that the Ramseys are innocent is in no way shape or form a proof, or evidence of an intruder. The intruder possibility stands apart as a seperate evidenciary consideration which could negate a belief of Ramsey innocence. But if that causes one to say, wait, the Ramseys can NOT be guilty, then that would show a bias was held, not a belief...also circular reasoning, if that bias confirmed the belief in an intruder. This could work both ways obviously.