DES MOINES, Iowa (AP) — A judge won't let a Des Moines woman use Iowa's new "stand your ground" defense against charges that she killed her stepfather.

The law says a person doesn't have to retreat before using deadly force if the person thinks his or her life is being threatened.

Sera Alexander's lawyer had argued that Alexander should be allowed to use the law although it took effect July 1, nearly two months after Anthony Hartmann was slain May 8. Alexander is accused of shooting to death Hartmann in the basement of her family's Des Moines home.

Judge Robert Blink said in his ruling issued Tuesday that Alexander could not use the defense "because that law was prospective in nature."

Police have said Hartmann didn't threaten or hurt Alexander immediately before he was shot.