The author of "An Occurrence at Owl Creek Bridge" does not describe what Farquhar was doing when he was arrested by the Union soldiers. The specific details are left up to the reader's imagination, probably because they would require a great deal of description which would detract from the dramatic interest of the story. No doubt Farquhar must have gone to the vicinity of the bridge on horseback and left his horse hitched to a tree at some little distance away. He might have brought something like kerosene, and he would have brought plenty of matches.
The soldiers would not be expecting Farquhar in particular. The Federal scout must have spread the same tale all over the region. But they would be on the lookout for some saboteur, and they would have pounced on Farquhar at about the time he was pouring his kerosene on the driftwood--assuming the Federal scout really was telling the truth when he said:
"I was there a month ago. I observed that the flood of last winter had lodged a great quantity of driftwood against the wooden pier at this end of the bridge. It is now dry and would burn like tinder."
However, there is no reason to believe what the Federal scout told Farquhar. If the bridge is of strategic importance and there are a lot of Union soldiers sitting around with nothing to do, then the officer in charge might have had all the driftwood cleared away at sometime during the past month. It would be simple enough to have the logjam broken up and the wood thrown into the flooded creek. In that case, Farquhar would be caught with a can of kerosene, a pocket full of wooden matches and possibly a bundle of rags, but that would be sufficient circumstantial evidence to hang him.
It is the second section of this story that tells us what Farquhar did in order to be captured by the Union soldiers and hung. This part of the tale represents a flashback to Farquhar's life before we meet him moments before his death on the bridge at the beginning of the tale. In this flashback we are told how he meets a man who was actually a Federal scout, who gives Farquhar the idea of destroying Owl Creek Bridge:
The soldier reflected. "I was there a month ago," he replied. "I observed that the flood of last winter had lodged a great quantity of driftwood against the wooden pier at this end of the bridge. It is now dry and would burn like tow."
Farquhar thus decides to try and destroy Owl Creek Bridge and is therefore ironically hung from it, as if to taunt him with his inability to succeed in this goal. As the Federal scout made clear, any attempt to destroy or damage this crucial bridge that allows the Union soldiers to supply their position with food, arms and men will result in execution. This is something that Farquhar finds out to his cost.