Upon arriving home, Utterson opened Lanyon's letter, which described in great detail what had happened. Jekyll asking for help, the drug... 

His identity. 

Utterson was baffled. There was no way that someone like Edward Hyde, the man wanted all throughout London, could be, or ever have been, the noble and gentle Henry Jekyll. He simply couldn't see it. 

But the other letter, Jekyll's, confirmed it.

Hyde was the product of an experiment

Hyde was the product of all those hidden impulses, all the vices, all the horrors and years of suppression, all contained within a single person. 

Utterson didn't know how to react, but he knew he would never see Jekyll in the same way again. 

He never would. 

But that didn't lessen the pity he felt for Jekyll. Yes, Hyde was a horrible person, but his friend was still inside him. And he wanted him back. 

So he returned to that familiar mansion, belonging to Dr. Jekyll. And there they were, Poole trying to coax Hyde into saying something, and the other man quieter than a tree. It was like talking to a brick wall. 

Utterson entered, his footsteps announcing his arrival. Hyde looked at him.

Hyde smiled, knowing perfectly well what Utterson knew now. But he was still quiet.

"Poole, you can go now." Utterson announced.

"Are you sure, sir?" he asked. 

"Yes, I'll take care of him. Oh, and don't tell anyone about this alright?" 

"But sir...He needs to get executed…" 

“I’ll deal with him. He will pay for what he did, but not yet. I’ll…keep him until he tells me what he did with Jekyll. Until then, don’t say anything, alright?” Utterson lied. “And keep searching for those salts, send them to me.”

“…Alright Sir.”

Then Poole left the room, leaving Hyde and Utterson alone.