The finale titled Opening Night concluded with the amateur detective trio played by Steve Martin, Martin Short and Selena Gomez figuring out who killed Ben  Selena's character Mabel Mora during the performance of the play realized that Clifford 'Cliff' DeMeo pushed Ben to his deathCharles-Haden Savage [Steve Martin] was surprised to see his stunt double Sazz [Jane Lynch] who arrived at the celebration wearing similar attire
See Details: Only Murders In The Building wraps season three on Hulu with case solved and another cliffhanger homicide