Dwight Cooper was a legally blind exterminator who came to realize that he could make far more money exterminating drug dealers than rats. His brother's gift of x-ray sight and his skill with a gun made Randall Cooper perfect for wiping out drug dealers on the orders of Dwight.
Dwight Cooper forced his secretary, Tammi Peyton, into becoming "involved" with him. His brother was obsessed with Tammi Peyton and when Dwight Cooper learned of her skimming of money, he sent Randall Cooper after her. Randall didn't obey his brother and ultimately sided with Tammi. When Dwight figured out that Tammi Peyton was skipping town he forced her at gunpoint to return to their offices.
He ordered his brother to execute Tammi and went out for a smoke. His brother knew Tammi Peyton wasn't coming back for him like she promised but he still loved her more than he ever loved his brother. He chose to shoot through the wall and kill Dwight Cooper. (TXF: "Surekill")