The mistake meant prosecutors went to trial unaware of 98.7 percent of the browser history records created that day.

Even the scant data the Sheriff's Office did manage to find showed computer activity inconsistent with the claim that Casey Anthony was awakened that morning to learn her daughter was missing and then drowned.

In his powerful opening statement, Baez described the resulting scene between father and daughter, after Caylee's wet, limp body was recovered.

"He immediately began to yell at (Casey). Look what you've done! Your mother will never forgive you and you will go to jail for child neglect for the rest of your fricking life."

So, the jury was told, George Anthony disposed of the body and both he and Casey re-launched their lives in a secretly shared compact of denial and deceit.

"This is strange," Baez told jurors. "This is bizarre. This is the life of Casey Anthony."

No, prosecutors countered, this was about the murder of Caylee Anthony – one accomplished, they claimed, with poison, suffocation and plastic bags.

Had Casey Anthony testified, as Burdick said she expected she would, prosecutors wanted to use the browser information to impeach her. But Casey Anthony never took the stand and the state did not elicit from any other witness even the skeletal browser evidence it did have.

Melich's spreadsheet does show activity from Casey Anthony's password-protected account beginning at 7:52 a.m., indicating that she was on MySpace and researching sexy costumes for "shot girls" to wear at her then-boyfriend's nightclub events.

But none of the 1,247 overlooked Firefox browser actions that day -- including the potentially incriminating search that afternoon -- appear in the easily extractable Explorer browser files that Melich relied upon for his timeline.

Investigators knew Casey Anthony preferred the family computer's Mozilla Firefox browser, but they previously had trouble decoding it, sheriff’s officials said.

In 2008, in a deleted section of Firefox browser records, they found searches from March 2008 for "how to make chloroform,” “neck breaking,” “death” and other terms after they requested that Osborn search the hard drive for the word “chloroform.” That request came after the Sheriff’s Office found traces of chloroform in the trunk where, they claimed, Casey Anthony hid her daughter's body.

But when Melich assembled his 114-line spreadsheet in 2011, he transferred data from the Internet Explorer browser that Casey Anthony rarely, if ever, used after March 6, 2008.

Melich and Osborne declined comment, and the then-head of the computer crimes section, Sgt. Kevin Stenger, has retired and could not be reached for comment.

But in a Sept. 6, 2012, email exchange with a Phoenix attorney who obtained the browser histories in August through a public records request, Osborne offered this explanation for the oversight: "I have a very good reason why (the foolproof suffocation search) wasn't brought up during trial. I was never asked to conduct a search for 'suffocation' and the word does not appear in the Internet artifacts we prepared for trial, unfortunately."

In a statement to Local 6 on Monday, the Sheriff's Office stood by Osborne and echoed her defense: “The Firefox record which contains the Google search for ‘suffication’ was neither extracted nor examined. A search for the keyword ‘suffocation’ was never requested from any OCSO investigator or the prosecutor’s office at any time during the investigation; therefore, this Internet record was inadvertently not discovered by Detective Osborne. … The agency has confidence in her knowledge and expertise in this very complicated field of computer forensics.”
When it comes to blame, the prosecution notes it requested the information from the Sheriff’s Office; the Sheriff’s Office states it was never asked to search for “suffocation.”

But both agree on this point: No one can say for certain whether the jury would have reached a different verdict if the evidence had not been overlooked.

Bringing the evidence to light

Repeated requests by Local 6 beginning in 2009 for a copy of the hard drive that contained the Internet histories were denied by the state attorney's office, which claimed -- correctly, it turned out -- it did not have the data in its possession.

Sheriff's computer investigators copied the entire hard drive from the Anthony's HP desktop computer after seizing it in July 2008 and gave prosecutors vague analysis of its activity and fragments of a minuscule amount of the vast information on them. The sheriff turned over the original hard drive to the Baez team in 2008 after it had been copied, Baez said.

After Baez revealed the "foolproof suffocation" search in his book, Phoenix attorney Isabel Humphrey requested and received a copy of the browsers’ histories from the Sheriff's Office.

Baez's theory that George Anthony did the search while contemplating suicide "was as crazy as the nanny story," Humphrey told Local 6, referring to Casey Anthony's original claim that a babysitter had kidnapped Caylee.

She obtained the data in August and turned it over to John Goetz, a retired engineer and computer expert in Connecticut. The pair had become acquainted online while following and discussing the case through the amateur sleuthing web community, Webslueths.

Using free software available on the Internet since 2004, Goetz said it took him less than two hours to extract more than 35,000 records detailing the computer's online activities from 2004 until it was seized in July 2008.

"Once you have converted the Internet history records, it really doesn't take more than 15 to 20 minutes to look through the entire Internet history for June 16," said Humphrey. "And I would think if there was one day you would pick to look at, that would be the day."