“Arrest the Jury,” read one sign outside the Orange County Courthouse in Orlando, Fla., on July 7, when Casey Anthony was sentenced to four years and fined $4,000 for four misdemeanor counts of lying to law enforcement.

The many Facebook pages devoted to criticizing the jury and its verdict have been even less diplomatic, bearing names like “Casey Anthony Jury Sucks” and “The Jury Failed Caylee.” Contributors were outraged that the panel acquitted Ms. Anthony of murdering her 2-year-old daughter, Caylee.