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.