Circumstantial evidence is evidence which may allow a judge or jury to deduce a certain fact from other facts which can be proven. In some cases, there can be some evidence that can not be proven directly, such as with an eye-witness.
In these cases, the prosecution will attempt to provide evidence of the circumstances from which the jury can logically deduct, or reasonably infer, the fact that cannot be proven directly. The prosecutor believes the fact can be proven by the evidence of the circumstances or "circumstantial" evidence.
In other words, in these cases it is up to the prosecutors to show through a set of circumstances that their theory of what took place is the only logical deduction -- that the circumstances can be explained by no other theory.
Conversely, in circumstantial evidence cases, it is the job of the defense to show that the same circumstances could be explained by an alternative theory. In order to avoid a conviction, all a defense attorney has to do is put enough doubt into one juror's mind that the prosecution's explanation of the circumstances is flawed.
No Direct Evidence in Peterson CaseIn the Scott Peterson trial, there is very little, if any, direct evidence connecting Peterson to the murder of his wife and unborn child. Therefore, the prosecution is attempting to show that the circumstances surrounding her death and the disposal of her body can be linked to only her husband.
But defense attorney Mark Geragos has apparently made great progress in shooting down or offering other explanations for the same evidence. For example, in the sixth week of the trial -- which is expected to last for months -- Geragos was able to debunk two key pieces of evidence that support the prosecution theory that the fertilizer salesman dumped his wife's body in San Francisco Bay.
The two pieces of evidence were homemade anchors Peterson allegedly used to sink the body of his wife and a hair from his boat that is consistent with her DNA. Under cross-examination, Geragos was able to get police investigator Henry "Dodge" Hendee to acknowledged to jurors that the prosecution's own expert witness had determined that a water pitcher found in Scott's warehouse could not have been used to make a cement boat anchor found in his boat.
Alternative Theories for the Same CircumstancesEarlier, photos presented by Hendee and questions from prosecutors tried to give the jury the impression that Peterson had used the water pitcher to mold five boat anchors -- four of which were missing.
One of the few pieces of evidence the prosecution does have is a six-inch dark hair found on a pair of pliers in Peterson's boat. Geragos showed Hendee two police photos taken in the warehouse, one showing a camouflage jacket in a duffle bag and another, showing it resting inside the boat.
Under Geragos' questioning, Hendee said the hair and pliers were collected as evidence after a crime scene technician took the second photo (with the jacket in the boat). The line of questioning from Geragos boosts the defense theory that the hair may have been transferred from Laci Peterson's head to her husband's coat to pliers in the boat without her ever being inside the boat.
As with all circumstantial evidences cases, as the Scott Peterson trial progresses, Geragos will continue to offer alternative explanations for each piece of the prosecution's case, in hopes of placing a reasonable doubt in at least one juror's mind.