He was apparently oblivious to everything but the fact that the pistol was there and that he had an opportunity to use it.
Ruth saw Warden and Lawler fighting in a corner.

Warden's back was against the wall, near the stove.

He was facing the door.

His lips were lacerated, drooling blood, his eyes were puffed and blackened, and he was screaming and cursing insanely.
As Ruth watched, her gaze taking in the wreck of the room--and Singleton picking up the pistol--she saw Lawler strike Warden--a full sweeping blow that sent forth a sodden deadening sound as it landed.
Warden sagged, his eyes closing as he slid to the floor and sat in the corner his legs doubled under him, his chin on his chest.
The scene had held only for an instant--merely while Ruth screamed.

The sound had hardly died away when Singleton succeeded in grasping the pistol.