I forgot Sagosto.

When they find Isaac here, Sagosto will either tell his story, which will be enough to convict me of this night's work, the REAL murder, even though I'm innocent; or else he'll blackmail me just as Isaac did." Jimmie Dale shook his head.
"You are doing Isaac's cunning an injustice," he said grimly.

"Sagosto was only a tool, one of many that old Isaac had in his power--and, for that matter, as likely as any one else to have had a hand in Isaac's murder to-night.

Sagosto saw you once when Isaac brought you into his place--not because Isaac wanted Sagosto to see you, but because he wanted YOU to see Sagosto.

Do you understand?
It would make the story that Sagosto came to him with the tale of the murder the next day ring true.