A Florida jury deliberated for more than 10 hours over two days after hearing 33 days of testimony.
She was charged with second-degree murder or manslaughter and was also charged with lying to sheriff's detectives investigating her daughter's 2008 disappearance.
The jury of seven women and five men had worked through much of the long weekend, hearing closing arguments Sunday and Monday morning and deliberating for six hours that afternoon. Jurors were chosen from the Tampa Bay area because of pretrial media coverage, and they have been sequestered in an Orlando hotel.
Prosecutors argued Monday that Anthony killed her 2-year-old daughter Caylee in June 2008 because the toddler interrupted her carefree partying and love life. The prosecution said the defense's assertion that Caylee's death was an accident made no sense.
Anthony's attorneys say the girl drowned in the family's pool. They have said Anthony panicked and that her father, a former police officer, decided to make the death look like a homicide by placing duct tape over the child's mouth and dumping the body in the woods. George Anthony has denied that.
Prosecutor Jeff Ashton told the jurors no one makes an innocent accident look like murder.
"That's absurd. Nothing has been presented to you to make that any less absurd," Ashton said. He also spent significant time reminding jurors about forensic evidence that he said links Anthony to her daughter's death, including the smell and chemical signature of decomposition in her car.
Lead prosecutor Linda Drane Burdick followed Ashton, telling the jurors that prosecutors presented every piece of evidence they promised in May during opening statements. Without saying it, she was pointing out that defense attorneys never presented direct evidence backing up their contentions that the child drowned.
She then hammered on the lies Casey Anthony, then 22, told from June 16, 2008, when her daughter was last seen, and a month later when sheriff's investigators were notified. Those include the single mother telling her parents she couldn't produce Caylee because the girl was with a nanny named Zanny - a woman who doesn't exist; that she and her daughter were spending time in Jacksonville, Florida, with a rich boyfriend who doesn't exist; and that Zanny had been hospitalized after an out-of-town traffic crash and that they were spending time with her.
"Responses to grief are as varied as the day is long, but responses to guilt are oh, so predictable," Drane Burdick said. "What do guilty people do? They lie. They avoid. They run. They mislead, not just to their family, but the police. They divert attention away from themselves and they act like nothing is wrong. That's why you heard about what happened in those 31 days."
Burdick concluded the state's case by showing the jury two side-by-side images. One showed Casey Anthony smiling and partying in a nightclub during the month Caylee was missing. The other showed a tattoo of an Italian phrase meaning "beautiful life," which Anthony got a day before her family and law enforcement first learned of the child's disappearance.
"At the end of this case, all you have to ask yourself is whose life was better without Caylee?" Burdick asked. "This is your answer."
Anthony sat stone-faced during much of the prosecutors' arguments, but occasionally shook her head in disagreement and spoke under her breath.
Defense attorneys claimed Anthony's lies and erratic behavior were brought on by her grief over her dead child and by her family's dysfunction. George Anthony has denied allegations from the defense's opening arguments that he abused his daughter, and the judge said no evidence has been presented to support it.
Defense attorney Jose Baez said during his closing argument Sunday that the prosecutors' case was so weak they tried to portray Anthony as "a lying, no-good slut" and that their forensic evidence was based on a "fantasy." He said Caylee's death was "an accident that snowballed out of control."
Baez began his closing argument Sunday with his biggest question: How did Caylee die? Neither prosecutors nor the defense have offered firm proof.
He attacked the prosecution's forensic evidence. He said air analysis of the trunk of Anthony's car, which allegedly showed air molecules consistent with decomposition, could not be duplicated. No one could prove a stain found in the trunk was caused by Caylee's body decomposing there. And witnesses showed maggots found in the trunk came from a bag of trash that was found there, he said.
Baez also attacked George Anthony as unreliable. He said a suicide note George Anthony wrote in January 2009 that claimed no knowledge of what happened to Caylee was self-serving and the attempt was a fraud. He said George Anthony claimed he was going to kill himself with a six-pack of beer and high-blood pressure medicine.