Why Can’t Some Juries Convict on Circumstantial Evidence?

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The jury's finding that Casey Anthony was not guilty of murdering her two-year-old daughter Caylee had many people confused as to how she “walked free” (not withstanding her convictions for lying to authorities). There were similar feelings when O.J. Simpson was found not guilty of murdering his ex-wife Nicole Brown Simpson in 1995. On the flip side, however, 10 years later, many spectators rejoiced when Scott Peterson was found guilty of murdering his pregnant wife Laci and their unborn child.

What do these high-profile murder cases have in common? All three juries were presented with a mountain of circumstantial evidence in support of conviction—but only one, the Peterson jury, found that proof of guilt was beyond a reasonable doubt. How is that possible?

The bottom line is that in each case, it was up to the members of the jury—as agreed upon by both the prosecution and defense—to weigh all the evidence presented and come to its decision. Indeed, this is the job of every criminal trial jury. And while different juries on the same set of facts and evidence could come to different conclusions, they all operate under the same judicial framework, as described below.

Beyond a Reasonable Doubt

As you probably know, the standard of proof in criminal trials is “beyond a reasonable doubt.” That is, the prosecution must prove that the defendant is guilty of the crime(s) charged to the extent that no reasonable person could have a reasonable doubt that the defendant is guilty.

Types of Evidence

The prosecution can prove guilt beyond a reasonable doubt by building a case through direct and/or circumstantial evidence.

Direct evidence “directly” shows the defendant's guilt, for example, a witness who testifies he saw the defendant committing a crime. Circumstantial evidence, on the other hand, is indirect evidence that may lead to the inference that the defendant committed a crime even though there is no direct proof, for example, a washcloth with the murder victim's DNA found at the defendant's house if the two didn’t live together.

Of course not all circumstantial evidence is created equal; some is stronger or weaker than others, and this is where jury discretion comes in. It is up to the individual members to weigh the importance of each piece of evidence and then come to a conclusion together as to whether the prosecution has proven guilt beyond a reasonable doubt.

One other important fact about circumstantial evidence: you may have heard somewhere that "there's only circumstantial evidence," implying that such proof isn’t enough to support a conviction, but that simply isn’t true. A defendant may be found guilty of a crime based solely on direct or circumstantial evidence, or a combination of the two.

Jury’s Role in Criminal Trials

As noted above, a jury’s job is to weigh all the evidence presented at trial. The jury is permitted to draw inferences from evidence, so long as they arise from proven facts and are logical and reasonable—they cannot be based on speculation. Indeed, juries are instructed that legally speaking, there is no distinction between direct and circumstantial evidence.

Circumstantial Evidence and Reasonable Doubt in Action

Taking the Anthony case as an example, the prosecution’s theory was that Casey Anthony used chloroform to suffocate her daughter. Unfortunately for the prosecution, though, the state of decomposition of Caylee’s body prohibited a definitive determination on the cause of death. Moreover, the prosecution had no “smoking gun” for the chloroform theory such as a bottle of the organic compound with Casey Anthony’s fingerprints on it. That could have been strong circumstantial evidence of guilt, but it just didn’t exist.

What the prosecution did have was Internet searches for information on chloroform from a computer in the Anthony house and traces of the substance in the trunk of her car. While the jury could have drawn an inference that these taken together, along with the fact that Anthony didn’t report that her child was missing for a month, proved that Casey Anthony used chloroform to suffocate her daughter—but they just didn’t feel they could find as such beyond a reasonable doubt.

At least one jury member has stated that the prosecution’s failure to definitively establish a cause of death created doubt in their minds. Moreover, regarding the chloroform specifically, Casey’s mother testified that it was she who had performed the searches, and an expert forensic witness for the defense refuted the prosecution’s experts’ testimony that claimed “shockingly high” levels of chloroform in the trunk by saying he only found low levels of it.

Accordingly, the jury concluded it was left with reasonable doubt regarding Anthony’s guilt of the most serious crimes charged and had no choice but to find her “not guilty.” Whether this decision was reasonable is likely to be debated for years to come.

Final Thoughts

It is important to note that our justice system is one that is based on the presumption of innocence until proven guilty and Blackstone’s formulation that it is "better that ten guilty persons escape than that one innocent suffer.”

Thus, the burden of proof for the prosecution is quite high; sometimes even with amazing advancements in technology, prosecutors aren’t able to convince a jury that the defendant’s guilt has been proven beyond a reasonable doubt—and sometimes the public disagrees with that decision. But public opinion doesn't matter to the justice system, and where there's reasonable doubt in the jury's collective mind, there simply can be no conviction.