Who Killed the Richest Man in the World?

A sniper fires through the window of the suite of the richest man in the world, who is planning on selling an oil lease to one of several bidders, each of whom was an expert marksman. Burke is informed that the bullet missed its intended target and killed, instead, the multimillionaire's personal bookkeeper. The tycoon constantly berates Burke for not having solved the crime to his satisfaction and insists on sending his staff along on the interviews with the suspects. After a bomb attempt again fails to kill the tycoon, Burke is almost shot by the sniper, who runs and falls to his death. Who hired him? - the Texan, the big game hunter, or the crazy brothers?