LAS VEGAS (AP) — The unprecedented move from MGM Resorts International to sue hundreds of victims of last year's mass shooting in Las Vegas using an obscure U.S. law never tested in court has been framed by the casino-operator as an effort to avoid years of costly litigation — but the legal maneuver may not play out that way.

The company is not seeking money in the lawsuits filed in at least seven states over the deadliest mass shooting in modern U.S. history. Instead, it wants federal courts to declare that it has no liability to survivors or families of slain victims under a federal law enac...