Who killed Monica Welles in rehearsal for murder?

Answer 1

It turns out, after declaring Leo Gibbs, the comedian, was the murderer, Alex Dennison shoots him. In the ensuing blackout and confusion, Frank Heller uses a flashlight to see where everyone is. He sees David and Karen standing calmly. The light finds Alex, who calls for lights. Alex helps Leo up and walks towards Frank. He asks where Frank got the flashlight. Frank says he was looking for matches in the desk. But, Alex already said Monica Wells didn't smoke. He reveals that Frank knew he'd find the flashlight, because he saw it the night he killed Monica. Alex goes on to reveal that everything Frank saw when he entered was scripted (although he admits a bit was improvised), and that all the other motives were made up. The cast chimes in their part in the whole thing, and how Alex figured out it was Frank. Frank's cab had records of leaving the theater and going to Monica's apartment. Slowly, as everything is unraveled, Frank confesses what happened that night. Monica died in an argument between them, and when he threw her, her head slammed against her desk. Frank faked the suicide, and Alex hired him to participate in his game, telling him it was Leo who was the killer. It turns out, Lieutenant McElroy was up in the light booth and arrests Frank. The ending contains much more info, but that's the basics.