what is mostly likely the meaning of red-handed as it is used in the following passage from paragraph 2?

His lash was always singing among the dogs, but it was of small avail. Directly his back was turned they were at it again. He backed up Spitz with his whip, while Buck backed up the remainder of the team. Francois knew he was behind all the trouble, and Buck knew he knew; but Buck was too clever ever again to be caught red-handed.