Who is Sam Harding from Night Probe! and what is their importance?

Sam Harding is employed by the New York & Quebec Northern Railroad in Wacketshire, New York. When he receives the information about the bridge being damaged, he is supposed to flag the train, but the train station is robbed, and the train passes through while he and Hiram Meechum are being held at gunpoint. After the robber leaves, Harding runs to the bridge, where he finds that the train has plunged into the Hudson River.