Los Angeles has created a gold standard policy for dealing with informants in the wake of a grand jury investigation that revealed hundreds of wrongful convictions. The city now has a “snitch registry” that tracks informants and a panel that reviews informants’ testimony before it can be used in court. But while states have explored similar rules, Virginia isn’t one of them, said Brandon Garrett, a University of Virginia law professor and author of “Convicting the Innocent: Where Criminal Prosecutions Go Wrong.”