When did the author hint to the reader that Roger was capable of something as horrible as murder?

We get our first hint that Roger is capable of murder as he look down upon Ralph and the others from the top of Castle Rock.

"Ralph bent back his head and glimpsed Roger’s dark face at the top."

(Page 251)

Then he lets the rock go.....

"High overhead, Roger, with a sense of delirious abandonment, leaned all his weight on the lever." (Page 260)