Roger is a fascinating character in the story, particularly because he represents the darker evil even more clearly than Jack. He begins as a boy who seems quiet, unwilling to engage but then quickly begins a precipitous slide into a sadistic and then murderous existence.
Some of the early hints about this tendency in him come when he follows Henry down the beach after kicking sand castles with Maurice and making some of the littluns cry. Roger follows Henry and when Henry stops to examine an area along the beach, Roger carefully begins to throw stones at him.
Roger is only testing the limits, however, as Golding writes that around Henry "was a space... perhaps six yards in diameter, into which he dare not throw." And the reason he did not throw within that space was that he still felt some restrictions of "the old world," where he'd lived in a civilized place with rules and police and powers that prevented him from acting on his most basic instincts. As Golding writes: "Roger's arm was conditioned by a civilization that knew nothing of him and was in ruins."
It will not take long for Roger to completely throw off the bonds of this old civilization and act on his sadistic impulses.