That he should be the means of bringing that terrible and active little man to an end seemed, as a matter of fact, absurd.

Guile must have played a part in that capture.
Suppose he were to tell the sheriff about the shooting of Uncle Bill?
That would be enough to convince men that Pete Reeve was capable of murder, for the shooting of Uncle Bill had been worse than murder.

It spared the life and ruined it at the same time.

But suppose he added his evidence and allowed the law to take its course with Pete Reeve?
Where would be his own reward for his long march south and all the pain of travel and the crossing of the mountains at the peril of his life?
There would be nothing but scorn from Uncle Bill when he returned, and not that moment of praise for which he yearned.

To gain that great end he must kill Pete Reeve, but not by the aid of the law.
"I dunno," he said to the sheriff who waited impatiently.