I take this explanation of why Consciousness of Guilt is considered by the majority to be a valid measure of one's guilt from ALBERTY v. U S, 162 U.S. 499 (1896).
The basic concept, as quoted from the Trial Court's Jury Instructions
It is a principle of human nature-and every man is conscious of it, I apprehend-that, if he does an act which he is conscious is wrong, his conduct will be along a certain line. He will pursue a certain course not in harmony with the conduct of a man who is conscious that he has done an act which is innocent, right, and proper. The truth is-and it is an old scriptural adage-'that the wicked flee when no man pursueth, but the righteous are as bold as a lion.' Men who are conscious of right have nothing to fear. They do not hesitate to confront a jury of their country, because that jury will protect them. It will shield them, and the more light there is let in upon their case the better it is for them. We re all conscious of that condition, and it is therefore a proposition of the law that, when a man flees, the fact that he does so may be taken against him, provided he does not explain it away upon some other theory than that of his flight because of his guilt.
'A man accused of crime hides himself, and then absconds. From this fact of absconding, we may infer the fact of guilt. This is a presumption of fact, or an argument of a fact from a fact.'
'Flight by a defendant is always relevant evidence when offered by the prosecution, and that it is a silent admission by the defendant that he is unwilling or unable to face the case against him. It is in some sense, feeble or strong, as the case may be, a confession; and it comes in with the other incidents, the corpus delicti being proved, from which guilt may be cumulatively inferred.'
The charge to the Jury in Hickory v. U. S., 160 U.S. 408, 16 Sup. Ct. 327, was even stronger:
in which a charge . . . was held to be tantamount to saying to the jury that flight created a legal presumption of guilt, so strong and so conclusive that it was the duty of the jury to act on it as axiomatic truth.
The Supreme Court offered this wisdom in response to the human inclination to believe that flight, or other behavior, is evidence in and of itself that the person committed the crime.
While, undoubtedly, the flight of the accused is a circumstance proper to be laid before the jury, as having a tendency to prove his guilt, at the same time, as was observed in Ryan v. People, 79 N. Y. 593, 'there are so many reasons for such conduct consistent with innocence that it scarcely comes up to the standard of evidence tending to establish guilt, but this and similar evidence has been allowed upon the theory that the jury will give it such weight as it deserves, depending upon the surrounding circumstances.'
We have seen in the Peterson case and the Kimble case that Detectives are very prone to basing suspicion on post-crime behaviors, assuming that any odd behavior is a consciousness of guilt. A common way of wording it for the husband of the victim is to say, He's not acting like a grieving husband. I have no objection to detectives noticing behaviors that seem out of the norm and putting someone through a thorough investigation based on this. However, a good detective knows that if the investigation does not produce independent evidence, then the seemingly abnormal behavior is not consciousness of guilt.
Jurors are very likely to have these same deeply-felt opinions about consciousness of guilt -- that certain behaviors are compelling evidence of guilt, even without any other evidence to support a conclusion of guilt. This propensity, coupled with blanket trust in police and prosecutors, will guarantee a conviction unless the Defendant is able to prove innocence. That is what the prosecutors count on.