Skip to main content

Flawed forensic evidence explains Casey Anthony acquittal, experts say

By Emanuella Grinberg, CNN
  • Lawyers, experts say forensic evidence was too experimental for courtroom
  • Method used to test air for decomposition made its courtroom debut in this trial
  • Testimony that hair came from dead body lacks proven scientific basis, experts say
  • Prosecutors say they respect verdict but still believe Caylee's death was premeditated

(CNN) -- As public outrage reaches critical mass over Casey Anthony's release from jail, trial observers who agreed with the jury's verdict say holes in the state's forensic case help explain why she was acquitted in daughter Caylee's death.

The strength of the state's forensic evidence, the stuff popularized in television dramas but widely misunderstood by the general public, has been a hot topic in legal and scientific circles since the discovery of Caylee's body in December 2008. With her remains decomposed to a skeletal state, could Florida prosecutors prove beyond a reasonable doubt how the 2-year-old died, or where her body had been before it was found in garbage bags in swampy woods near the Anthony family home?

They turned to cutting-edge forensic evidence that Anthony's lawyers called "junk science" and others considered too experimental for the courtroom.

One blogger summed up the thoughts of many trial observers in a blog post titled, "The real danger from Casey Anthony's trial: Scary scientific precedents."

"Most of these forensic techniques have never tp://been allowed in any trial in the U.S.," blogger Matt McCusker wrote on the website of the American Society of Trial Consultants, Deliberations. "The average juror does not have the expertise to differentiate between 'good science' and 'junk science,' so the court must help them by excluding dubious evidence." He made the observation a day before the not guilty verdicts.

But, with the verdicts, many believe the jurors showed they didn't buy the evidence, and proved the system works.

"One of the debates among people who are concerned with junk science in the courtroom -- or evidence coming in before there's proof that it means what the expert says it means -- is whether juries are better or worse than judges at scrutinizing forensic evidence," said professor Adina Schwartz with the Department of Law, Police Science and Criminal Justice Administration, John Jay College of Criminal Justice.

Anthony juror: We didn't buy drowning
What's next for Casey Anthony?

"But it seems this jury was capable of scrutinizing the forensic evidence and not just being blown away by it. It's very cheering to see a jury follow the law and the directions of the court."

A juror who spoke with ABC News after the verdict said the state's case left too many questions unanswered, leading to the decision to acquit Anthony on murder charges. She was convicted of four counts of lying to police and is set to be released Sunday.

"If you're going to charge someone with murder, don't you have to know how they killed someone or why they might have killed someone, or have something where, when, why, how?" said Jennifer Ford, who was juror No. 3.

In the aftermath of Anthony's acquittal, investigators who spent months interviewing witnesses and combing the area for evidence defended their work.

"In every case, especially a case with this many witnesses and this much evidence, you can always look back and improve on what you've done. I don't know that anyone up here could think of anything that we could have done differently that might have affected the outcome," Orange County Sheriff's Office Sgt. John Allen said in a press conference Tuesday. "We worked very hard on this case."

Casey Anthony investigators defend case to reporters

While Florida prosecutors respect the jury's verdict, they're still confident in their theory of the case: Caylee's death was premeditated and carried out by her mother.

"If [the jury] did not see in the photographs of how Caylee was found what we saw, and what other people see, then that's fine. We shall agree to disagree," Assistant State Attorney Jeff Ashton told CNN's Piers Morgan. "I have never been able to figure out a reason why somebody would cover up an accident by putting pieces of duct tape over the nose and mouth of a child and then dumping them in a swamp. When children die by accident, people call for help. That's how it works in the real world. In the fictional world that may be different. But in the real world, people want their child to live and Casey clearly didn't. Every action she took showed that."

"I wouldn't call it all junk science, but it wasn't ready for court."
--Keith Murray, defense lawyer and forensic consultant

Judge Belvin Perry held hearings in March and April to determine the admissibility of the scientific evidence. Known as a Frye hearing, the proceeding takes its name from the state court case that established the inadmissibility of polygraph tests in criminal trials. Perry heard testimony to determine if the forensic evidence met the standard of being "generally accepted" by a meaningful segment of the relevant scientific community.

Casey Anthony back in court for more arguments over evidence

A method used to prove the chemical existence of decomposition in the trunk of Anthony's car made its debut outside the lab at her trial, according to testimony from its creator. A rare method of analyzing a strand of hair for signs of decomposition also was presented to the jury, much to the surprise of forensic scientists and lawyers watching the case.

"The judge really opened the doors for everything in this case. Maybe he thought, 'Let the appeals court deal with it.' Maybe he was punting. But in my opinion, none of it should have gotten into the trial" said defense lawyer and forensic consultant Keith Murray.

"I wouldn't call it all junk science, but it wasn't ready for court, and just by letting it in doesn't mean the jury's going to buy it. I'm sure we'll see more of this stuff down the road; hopefully it'll be more refined by then. It just wasn't ready for prime time."

Was Caylee's body in Casey's trunk?
Casey Anthony car odor testimony

Jurors in the case got a crash course in DNA, hair analysis and chemistry as prosecutors called witnesses to support their theory that Anthony used chloroform on her daughter to render her unconscious, placed duct tape over her mouth and nose and kept the body in the trunk for several days before disposing of it.

Prosecutors acknowledged their case was largely circumstantial, due to the decomposed state of Caylee's remains, which were found more than five months after she was reported missing in July 2008. To link Anthony to a homicide, they attempted to prove the presence of a decaying corpse in her trunk.

Arguably, the most disputed testimony came from Dr. Arpad Vass, the inventor of a new method of testing air for chemicals indicative of decomposition. Vass, a forensic researcher at Tennessee's Oak Ridge National Laboratory, also does research at a University of Tennessee outdoor laboratory -- popularly known as the "the body farm" -- where human corpses are left to decay while scientists study the decomposition process.

Vass told the jury that testing of air samples, carpet, scrapings from the wheel well and a spare tire cover from the car found a handful of compounds associated with human decomposition.

Vass also said testing showed chloroform present at a "shockingly high" level on a carpet sample from the trunk. Defense experts, including an FBI lab technician, disagreed and said they found low amounts of the substance, which is also present in a number of household cleaning products.

Vass testified that he owned a patent on the technique, which had not been used in a homicide investigation before this one. That alone should have been grounds to exclude it from testimony, based on a lack of established scientific validity, forensic consultants and defense lawyers said.

"A courtroom isn't a scientific lab and evidence shouldn't come in before it has been accepted in a relevant scientific community," Schwartz said.

Vass acknowledged several shortcomings in his testing that detracted from its credibility: He didn't collect the samples, someone in Florida did, and sent them to his lab in Tennessee; as controls in his analysis, he used chloroform obtained from two vehicles unrelated to the case; after obtaining readings from the samples, he compared them to a proprietary database that was not revealed to the defense.

Vass' stark characterizations of his findings also troubled trial observers: How could he unequivocally state that his findings meant that a human body had been in the trunk?

Scientist: Body in Casey Anthony's trunk 'only plausible explanation'

"He comes in and says, I have invented this new air analysis system and I can tell this is a decomposing body. He didn't say it was consistent, he said it had to be a decomposing body. That's the kind of grandiose claim that you can pretty much never make in forensic science because we don't yet have the research and facts to back it up," Schwartz said.

The National Research Council addressed the issue of scientists overstating their analyses in a 2009 study, "Strengthening Forensic Science in the United States: A Path Forward." The report concluded that the nation's forensic science community suffered from a dearth "of strong standards and protocols for analyzing and reporting on evidence" and "peer-reviewed, published studies establishing the scientific bases and reliability of many forensic methods."

In light of those shortcomings , the committee concluded, any forensic testimony should be couched with a strong disclaimer describing the limits of the analysis.

"The simple reality is that interpretation of forensic evidence is not infallible -- quite the contrary," said the committee. "Exonerations from DNA testing have shown the potential danger of giving undue weight to evidence and testimony derived from imperfect testing and analysis."

Nuclear DNA stands above the rest of the forensic science disciplines in terms of reliability, the report said, "not only because the chances of a false positive are minuscule, but also because the likelihood of such errors is quantifiable."

Nuclear DNA analysis was not used to test a piece of hair found in the trunk that the state said belonged to Caylee.

Mitochondrial DNA testing was used to determine the origin of hair, which state experts said had a single decomposition band near the root. The method is used when a specimen may not contain enough nuclear DNA for testing, FBI forensic examiner Catherine Theisen testified for the state.

Nuclear DNA is inherited from both parents and can identify a person to the exclusion of all others, Theisen testified. Mitochondrial DNA is inherited maternally, meaning it is the same for all maternal relatives and siblings in a family -- in Casey Anthony's case, her mother, Cindy Anthony, her grandmother and her brother, Lee Anthony.

Forensic examiner: Neither Casey nor Caylee can be excluded as source of hair

Expert links hair evidence to Caylee
Homicide or accident?

"The fact that the mitochondrial DNA pattern matched Caylee's did nothing to show that it didn't match her mother or her grandmother or any other relatives from the maternal line," Schwartz said. "I think it should have been excluded on relevance; its existence didn't make it more or less probable that Caylee was in there, and you don't admit evidence if the danger of unfair prejudice outweighs the probative value."

Moreover, post-mortem root banding is rarely introduced as evidence in courts of law because there is no conclusive scientific explanation for what causes it, said Murray, the forensic consultant.

"We don't know what biological mechanism causes post-mortem root banding. The FBI lab technician asserted that it can only be attached to dead bodies, but there are other environmental factors that can cause similar root banding that looks pretty identical," he said. "The witness acknowledged that in the trial and during the Frye hearing."

Evidence from the car wasn't the only point of contention. There was also Caylee's skull, a piece of duct tape and what they could tell investigators.

Crime scene photos didn't offer much clarity. Some showed the skull with a piece of duct tape around the lower facial region. In others it appeared to be lying alongside the skull.

Prosecutors contended that Anthony placed the duct tape over Caylee's nose and mouth. To support that theory, they used a video demonstration of an image of Caylee's decomposing duct-taped skull superimposed over a photograph of the toddler cheek-to-cheek with her mother as they both smiled.

Jurors watch graphic video in Casey Anthony trial

Defense lawyers argued that the demonstrative aid was unfairly prejudicial. The judge sided with prosecutors, who said that aid was necessary to show the tape was large enough to cover Caylee's nose and mouth.

"It was a graphic animation portraying how the child was killed but it wasn't evidence. It only graphically showed what the prosecution would like the jury to believe happened. It's not evidence, it shouldn't have been admitted as evidence. It's inflammatory and not based on any scientific foundation," said Lawrence Kobilinsky, chairman of the Department of Sciences at John Jay College School of Criminal Justice in New York.

"I think, if she was convicted, it would have been grounds for reversal. It's inflammatory, based on a hunch, and does not prove duct tape was used to kill the child."

Because of its condition, no DNA evidence was detected on the duct tape, leading defense witness Werner Spitz to conclude the tape had been placed on the skull after her death.

Defense lawyers claimed that Roy Kronk, a meter reader who stumbled upon the burial site, put the duct tape there to keep the jaw attached to the skull.

The jury also heard about a "phantom sticker" that supposedly left residue in the shape of a heart on the duct tape. No sticker was found on the duct tape, but prosecutors introduced a sheet of heart stickers found in the Anthony home into evidence in an effort to connect the mother to the duct tape.

Examiner: Heart-shaped adhesive found on tape covering Caylee's mouth

An acquittal ensures there will be no appeal. To some, that's good news, even if they were concerned by what they saw and heard in the trial.

"This jury did its job and it's a good thing," said Schwartz, Kobilinsky's colleague at John Jay. "They didn't say Casey Anthony was innocent; they just said the prosecution didn't prove its case. Like it or not, that's how our system works, because we are talking about someone's life and liberty."