In December, the state's attorney's office filed court papers indicating that prosecutors would not seek the death penalty in connection with the first-degree murder case.
In a notice of intent filed today, prosecutors said additional information has become available. The filing says that "sufficient aggravating circumstances exist to justify the imposition of the death penalty," according to the Orlando Sentinel.
A spokeswoman for Jose Baez, Anthony's attorney, said in a statement, "This is not a death penalty case. We will do whatever is necessary to defend Casey Anthony from the state trying to take her life. We already have death-qualified defense lawyers on our team and are prepared for a vigorous defense."
Anthony, 22, has pleaded not guilty in the death of her daughter, Caylee. She is scheduled to go on trial in October.
The child's remains were found Dec. 11, less than a quarter-mile from the home she shared with her mother and grandparents.
The case started with a frantic emergency call from Casey Anthony's mother, Cindy Anthony, in mid-July.
On the tape, she is heard frantically telling emergency operators, "I can't find my granddaughter. … There's something wrong. … I found my daughter's car today and it smelled like there's been a dead body in the damn car." Casey Anthony then got on the phone and reported she may have a missing child.
Cindy Anthony later retracted that statement, saying that the smell in the car could have been from garbage.
As investigators quickly learned, this would only be the first of many twists and story changes in the curious case.
CLICK HERE for a timeline of the case.
In the original version of events, Casey Anthony reported her missing to police, saying she had dropped the child off at a baby sitter's house June 9. When she went to pick the child up, both the child and the baby sitter had disappeared.
Casey Anthony's parents both corroborated the story until a bond hearing July 25 when Cindy Anthony said that the last time she saw the child was not June 9, but June 15, and that she had just been confused.
When police questioned Casey Anthony about her daughter before her arrest, they say she misled them multiple times.
The Phantom Baby Sitter in Casey Anthony Case
When she took police to the apartment where she said baby sitter Zenaida Fernandez-Gonzalez lived, they found that no one had lived in the apartment for five months.
At that time, investigator Yuri Mellich of the Orange County police department said, "I am not disregarding that this person may or may not exist, but Casey Anthony's friends and family have never met this person."
After an extensive search for Gonzalez, a woman with the same name came forward in September to tell authorities she had never met Casey Anthony or Caylee. Police cleared her of any involvement.
In a police report, Mellich said that "after several months of investigation, detectives could find no one who has ever met, spoken with or seen any Zenaida Gonzalez who had cared for Caylee Anthony."
Casey Anthony also claimed to have worked for Universal Studios, but admitted later that that was not true.
Scientists found evidence of body decomposition and traces of chloroform in Casey Anthony's car trunk, according to forensics reports released in October.
Lab reports from the FBI found that a hair strand in the trunk showed "characteristics of apparent decomposition." The hair is "microscopically similar" to hair strands found on Caylee's brush, but the report said it could not conclusively say the hair in the trunk had come from the missing girl.
Casey Anthony had been considered a "person of interest" in her daughter's disappearance since mid-July after police reported in a bond hearing that they believed they'd found evidence of decomposition in the car.
But what unsettled investigator Carlos Padilla more than Casey Anthony's imprecise information was her overall attitude.
"She has shown no emotion," Padilla told ABCNews in July. "That's unusual. At the time of the interviews … she didn't seem concerned and that made this case much stranger."
"She spoke to deputies like she was talking about baseball. How do you get through to someone like that?" he said.
But Casey Anthony revealed an entire range of emotion in videos of jailhouse conversations between her and her parents, which were released Dec. 5.
In the more than 300 minutes of video released by the Orange County Sheriff's Department, Casey Anthony is shown laughing, crying and growing frustrated with the investigation and her family's questions.
When Cindy Anthony confronted her with Mellich's suspicions that she had had something to do with Caylee's disappearance, her daughter dodged the issue.
"Yuri [Mellich] has it set in his mind. He thinks you've done something to Caylee," Cindy Anthony said to her. At that point, her daughter got up and, when she returned, steered the conversation in a different direction.
Casey Anthony also said that she knows the conversations are being recorded and "there are things [she] directly needs to say" to each of her parents.
When gruesome details about the discovery of Caylee's remains were released in January, Casey's father, George Anthony, nearly committed suicide.