Speaking from the Grave: The Dead Witness, I

Action against D Supermarket for injuries allegedly sustained when P slipped and fell while shopping in the D store. P claims he slipped on ketchup from a broken bottle. Dclaims P slipped on a wad of tobacco from P's mouth. W, a customer in the store who rushed to P's aid while P was lying unconscious on the floor, is P's first witness at trial. Wtestifies that she saw ketchup on the soles of P's shoes after the fall. On cross-examination defense counsel questions W's perception, memory, and veracity but fails to make much progress. Verdict is for P, but when the jury is polled it is discovered that the panel consists of only 11 people. A mistrial is declared. On retrial, P introduces evidence that W is dead and calls R, the court reporter from the first trial, to testify that he remembers W's former testimony and to relate it. D objects. What ruling and why?

What policies justify the use of former testimony of an unavailable witness? What are the dangers and drawbacks of the use of this type of evidence? What limitations should be imposed on the use of former testimony?