The Collaborative International Dictionary
                    Corroboratory
                    
                        
                
                                                                    Corroboratory \Cor*rob"o*ra*to*ry\ (-t?-r?), a. Tending to strengthen; corroborative; as, corroboratory facts.
Wiktionary
                    corroboratory
                    
                        
                
                                                                    a. Serving to corroborate or strengthen
WordNet
                    corroboratory
                    
                        
                
                                                                    adj. serving to support or corroborate; "collateral evidence" [syn: collateral, confirmative, confirming, confirmatory, corroborative, substantiating, substantiative, validating, validatory, verificatory, verifying]
Usage examples of "corroboratory".
Besides, if Forte did die in that crash, if there was a crash, we'll be able to provide corroboratory evidence to that effect.
Once Ames said, perhaps to break the tension of waiting, "How could they be sure of picking up this Struthers, from the next estate down the road, so they'd have an outside, corroboratory witness?