MIAMI — Assertions by the prosecution that Casey Anthony conducted extensive computer searches on the word “chloroform” were based on inaccurate data, a software designer who testified at the trial said Monday.

The designer, John Bradley, said Ms. Anthony had visited what the prosecution said was a crucial Web site only once, not 84 times, as prosecutors had asserted. He came to that conclusion after redesigning his software, and immediately alerted prosecutors and the police about the mistake, he said.

The finding of 84 visits was used repeatedly during the trial to suggest that Ms. Anthony had planned to murder her 2-year-old daughter, Caylee, who was found dead in 2008. Ms. Anthony, who could have faced the death penalty, was acquitted of the killing on July 5.

According to Mr. Bradley, chief software developer of CacheBack, used by the police to verify the computer searches, the term “chloroform” was searched once through Google. The Google search then led to a Web site, sci-spot.com, that was visited only once, Mr. Bradley added. The Web site offered information on the use of chloroform in the 1800s.