Roth had deals with Claude Wome for diamonds imported from Africa, one time leading to being arrested.
Events of GTA IV
The Diamond Deal
Roth also had connections with Pegorino Family Capo Ray Boccino. He entered a deal with Ray, which took place in the The Libertonian. Isaac, Mori and two others stood face-to-face with the two men dealing for Ray, Johnny Klebitz and Niko Bellic. While Mori was looking at the diamonds, Luis Fernando Lopez shot Mori from a window overlooking the transaction. Isaac ran to Mori's side and tried to help him but when he realized he was dead, he snatched the diamonds and ran while Johnny took the money. Soon Isaac was caught and knocked out by Luis, who then stole the diamonds and took them to Gay Tony.
Isaac thought the ambush was set up by Ray and threatened to have him killed. In retaliation, Ray sent Niko to kill Isaac at his base in the Majestic Hotel.