Police who investigated the disappearance of Casey Anthony's two-year-old daughter admitted today that they overlooked a Google search for 'fool-proof' suffocation on the day the girl was last seen alive.

Captain Angelo Nieves said on Sunday that his office's computer investigator missed the June 16, 2008 Internet search. 

It is not known who performed the search but it was allegedly done with a browser primarily used by the two-year-old's mother, Casey Anthony, who was acquitted of the girl's murder in 2011.

Whoever conducted the Google search looked for the term 'fool-proof suffication', misspelling 'suffocation', and then clicked on an article about suicide that discussed taking poison and putting a bag over one's head.

The browser then recorded activity on the social networking site MySpace, which was used by Casey Anthony but not her father.

A computer expert for Anthony's defense team found the search before the trial. Her lead attorney, Jose Baez, first mentioned the search in his book about the case but suggested it was George Anthony who conducted the search after Caylee drowned because he wanted to kill himself.

Not knowing about the computer search, prosecutors had argued Caylee was poisoned with chloroform and then suffocated by duct tape placed over her mouth and nose. The girl's body was found six months after she disappeared in a field near the family home and was too decomposed for an exact cause of death to be determined.

Prosecutors presented evidence that someone in the Anthony home searched online for how to make chloroform, but Casey Anthony's mother, Cindy, claimed on the witness stand that she had done the searches by mistake while looking up information about chlorophyll.