Crime-scene investigator Jennifer Welch holds up duct tape entered as evidence during Day 16 of Casey Anthony's trial at the Orange County Courthouse in Orlando, Fla., on June 11, 2011
Millions of viewers have been transfixed by the parade of forensics experts presented by the prosecution over the past few weeks in the trial of Casey Anthony, a 25-year-old mother who stands accused of killing her 2-year-old daughter Caylee and dumping the body near their Orange County, Florida, home in 2008. The ubiquitous broadcasts of the trial are as compelling as anything that fans of the fictional forensics drama CSI: Miami might encounter. But the cutting-edge crime-scene science is far more technical, inexact and contradictory than anything a screenwriter might gin up. And it's just those contradictions that the defense will point out as they take center stage this week.
To find out how Anthony's lawyers might rebut the most damaging evidence presented by the prosecution, TIME asked crime experts to weigh in on the viability of seven aspects of the forensics testimony.
1. Evidence that is "consistent with" a crime does not constitute proof
On TV, forensics scientists usually emerge from the lab with proof of the killer's identity. DNA, fibers, hair samples and a host of other evidence always seem to point fictional cops to the culprit.
But in reality, it's not usually about one hair sample. In the Anthony case, the prosecution has attempted to show that the evidence they've gathered is "consistent with" their theory of how Caylee was killed. Prosecutors allege that Anthony conducted Internet searches for making chloroform, used the homemade chemical to knock her daughter out, put duct tape over Caylee's mouth and nose and then dumped the body in the woods. Many of the experts in the case so far have testified that the evidence they've seen is "consistent" with these assertions.
But consistency is not as powerful in court as presenting evidence that points directly to the identity of a killer, explains Adina Schwartz, an expert in evidence law and science and a professor of law and philosophy at the John Jay College of Criminal Justice, City University of New York. "What does 'consistent with' mean? It means 'could be,' " she says. That uncertainty will create room for the defense to make its case.
2. Identifying human hairs isn't an exact science
According to the prosecution's narrative, Anthony stored the body of her daughter in the trunk of her car after subduing the girl with chloroform.
Investigators discovered hairs in the trunk, which they tested for DNA. This would be the part of the TV plot where we'd learn who owned the hairs. In reality, DNA testing only narrowed the identity. Because the hairs they found contained no roots or tissue, investigators could test only for mitochondrial DNA, which is passed down through female ancestors. This means the hairs could belong to as many as five people: Casey, her mother, grandmother and brother, and finally Caylee.
"They cannot say with scientific certainty that it's Caylee's, although it's suggestive that it's Caylee's," Lawrence Kobilinsky, a DNA expert and head of the forensic sciences department at John Jay College, says of the hairs. (Kobilinsky consulted with Anthony's defense lawyer Jose Baez on the initial part of the case but has since stopped working on it.)
The hairs in the trunk had dark bands near the base, which prosecution experts testified indicate a decomposing body. Kobilinsky says the bands can also be caused by air pockets. "There are people that claim they can tell a difference, and so this may become an issue at trial," he says. "But this calls for subjective determination." In other words, two experts examining the same hair could have two opinions: that the darkening was caused by either decomposition or air pockets.
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