The person who killed dusty could have been anyone of these people, they all had motive but only one of them was desperate enough to kill one of his closest friends. (7:20)The murderer must have been wearing gloves when he set the table again because he left traces of sodium, carbon, iron, and gold. When the Murderer saw his chance, he took it. 7:25)Right when the table had been set and no one was around he slipped the Potassium cyanide into Dustys cup. Now potassium cyanide is a hard thing to come by and only someone who had worked with it for many years would have known the right amount to give to Dusty to make him drop dead. (7:35) Dusty returns down stairs to finish his breakfast. (7:40) Dusty takes one drink then five minutes later he drops dead. Now let me fill you in on how all this evidence plays into this. Mr. Horace Throat had been experiencing some money problems with the mob and really need this auction to go well.
Horace was counting on Dusty to help him out but when he let him down, he snapped. Horace had been working in metal finishing for many years and he used the same gloves as he did to work as he did to place the cyanide in the drink, which is how the traces of gold ended up on the table. Second Dusty was the only one of that group of people who had already had potassium cyanide on him because he was already doing work for Dusty. Horace Throat killed one of his closest friends and best buyers of many years just for money to pay off the mob.