John Bradley told The New York Times assertions by the prosecution that Casey Anthony conducted 84 computer searches on the word "chloroform" were based on inaccurate data.
Bradley was the chief software developer of CacheBack, a program used by police to verify Casey Anthony's computer searches.
The prosecution repeatedly used the finding of 84 visits to suggest that Anthony planned to kill her 2-year-old daughter Caylee.
Bradley said after redesigning his software he discovered that Anthony visited what the prosecution called a crucial Web site only once, not 84 times.
His findings were not presented to the jury and the record was never corrected, he said.
"I gave the prosecution everything they needed to present a new report," he said.
Casey Anthony was acquitted of causing Caylee's death July 6.
One of her attorneys said it was "outrageous" that prosecutors withheld critical information.
The Times said the state's attorney's office in Orlando did not return messages seeking comment.