In a criminal case, a demurrer is a defendant's assertion that the document laying out the charges—the complaint, information, or indictment—is legally insufficient. In demurring, the defendant claims that the charging document is so flawed that it can't be used to convict him or her.
A demurrer involves a consideration of the document itself—not any of the evidence. Some demurrers go to the heart of the charging document by alleging that it fails to state an offense, while others challenge its form—for example, by arguing that it's too vague or uncertain.
Demurrers usually occur at or before the time for entering a plea. If the court grants a demurrer, the prosecution can typically re-file charges. Similarly, some errors are so minor that the prosecution or judge can simply edit them and otherwise leave the charging document intact. But sometimes the demurrer reveals an underlying problem with the prosecution's case that can't be fixed.
Example: The prosecution charges Walter with a statute that penalizes violation of the terms of a family violence order. But the complaint doesn't indicate the terms that he allegedly violated or the manner in which he violated them. It doesn't specify, for example, that he came to the family home when prohibited from being there, or that he came within a prohibited distance of his estranged wife. The court grants Walt's demurrer. (Newsome v. State, 296 Ga. App. 490 (2009).)
Example: Gus files a demurrer to a complaint that accuses him of threatening Walter in violation of a statute that prohibits "criminal threats." Gus claims that the statute is unconstitutional because it infringes free speech, and that the complaint is therefore void. The judge rejects this argument on the grounds that previous courts have rejected similar claims; they've held that the Constitution doesn't protect all kinds of "speech."
Example: In a theft prosecution, Saul argues that the complaint is faulty because it doesn't provide the name of the owner of the allegedly stolen property. But Saul didn't raise this technical argument until after pleading to the indictment, so the court deems it "waived." (Lanier v. State, 269 Ga. App. 284 (2004).)