They took in abondened puppies that they forced to steal food for them. If the pups started to rebel against them, they were killed without mercy. Kuro lost his life that way, but the brother, Hook, managed to escape. Even Mel was close to be killed before Weed, GB, Lenny, and Hook with help came to the rescue.
In the anime, the Trio was the leaders of a small pack instead of just themselves, as well as it was Smith that helped them instead of Lenny and other dogs.