The evidence to convict Paul consisted of fingerprints on the gun, the fireplace poker, and Gino's St. Christopher medal keychain. However, no prints were lifted from Phyllis' note she placed in Gino's pocket, which would not have had Gino's prints on it since she never handed it to him. Further, Phyllis believed Emma committed suicide by taking the missing pills, yet the police took no prints from the pill box which would have confirmed that Emma had handled it and possibly did take some of the pills on her own.
The police pick Sanford up for questioning based on the cook's description of him as the man who helped Phyllis carry Emma back to bed after her stroke. But the police don't ask him any questions when he enters the office; only the priest does. The police would have interviewed the priest first, and then questioned Sanford afterwards.