Orange County Sheriff Jerry Demings also revealed that prosecutors were considering perjury charges against Anthony's mother, but a spokeswoman for the state attorney's office later said they would not be pursued.
Casey Anthony was acquitted a week ago on charges of killing her 2-year-old daughter Caylee in 2008. Anthony was found guilty on four charges of lying to law enforcement officers. She is to be released from jail Sunday.
The sheriff held the news conference to defend his investigation and because his office had been besieged with interview requests since the verdict.
"The ultimate goal ... is that our personnel can get back to work doing the business of the taxpayers and residents of Orange County," Demings said. "This is the only way that we can move forward."
Demings wouldn't say who was accused of witness tampering, but it didn't involve Casey Anthony's mother, Cindy. She stunned prosecutors during the trial when she testified that she had done searches for chloroform on the family's computer. Prosecutors believed, along with sheriff's investigators, that Casey Anthony had performed the search as she plotted to kill Caylee.
Later, testimony by two of Cindy Anthony's co-workers that the company's electronic records showed that she was logged into her work system for most of the day on both March 17 and March 21 when the chloroform searches were done.
Cindy Anthony said she had performed the Internet searches for chloroform while looking up information on chlorophyll, a green pigment found in plants. Chloroform is a chemical that can be used as a sedative and is fatal to children in small doses.
A co-worker said the system would not have recorded Cindy Anthony's presence if a person hadn't been actively using the work computer.
The government presented evidence at trial that chloroform was found in Anthony's car trunk and insinuated that she could have used it to render Caylee unconscious.
As for the alleged witness tampering, detective John Allen would only say the sheriff's office has interviewed some witnesses.
"In regards to where we will go, it really depends on what information we get and what people come forward to provide additional information," Allen said.
The investigators at the news conference sat at a table alongside a big picture of Caylee. The sheriff said it was a reminder of what his investigators were pursuing during the three-year case that dominated his resources.
"This is what this was all about," Demings said. "It was about a missing child. That's what motivated our staff and our community."
Demings said his office followed up on more than 600 tips and worked with more than 100 FBI agents. He said he is still in the process of working with his accounting department to total up substantial investigative costs. Prosecutors want Anthony to incur those costs because they said the lies she was convicted of telling investigators directly led to the expenditures.
"Obviously those were resources that could have been put toward finding other missing children," Allen said.
Texas Equusearch, the private group that conducted several searches for Caylee in 2008, filed a lawsuit against Anthony on Tuesday, seeking $15,000 for what it spent on searches. The lawsuit claimed Anthony made misrepresentations to the group's founder, causing extensive, costly and time-consuming searches for Caylee.
Anthony's defense said Caylee accidentally drowned in the family pool and her father, a former police officer, helped cover it up. Anthony's partying and shopping during the month before her daughter was reported missing was caused in part by her father's sexual abuse, her attorneys said.
George Anthony denied the claims in court, and investigators said Tuesday they were rebuffed by the defense team when they tried to interview her about the allegations.
Allen and the case's lead detective, Yuri Melich, said they wouldn't do anything differently in the case, despite not winning a conviction.
"Ultimately, it's up to the jury to decide," Melich said. "We respect that and honor that."
The sheriff did acknowledge that finding Caylee's remains earlier could have built a stronger case. The remains were found by a meter reader in December 2008, six months after Caylee was reported missing. The meter reader initially called authorities as early as August about seeing what might have been a skull in the woods.
Demings said the investigator called out after the meter reader's report no longer works at the sheriff's office, and he believed authorities correctly focused on Anthony.
"I certainly don't have any doubt," Allen said. "... I think our work was solid."