Records show investigators received a tip that Anthony Rusciano knew Caylee's mother but when questioned he said he had only met her in passing at a party, the Orlando (Fla.) Sentinel reported Wednesday.
Investigators said they learned Rusciano allegedly hadn't told them the truth after conducting a forensic analysis of the computer belonging to Caylee's mother, Casey Anthony.
Rusciano, who joined the sheriff's office in February, was still on probation when he was fired Friday.
Caylee Anthony has been missing since June. Police have charge her mother with child neglect and named her a person of interest in the girl's disappearance.