After Louis Azarello informed the police of Fusco's involvement with Stills and HR, Soriano started investigating him. He cornered Fusco at the station and took his badge and gun. He told Fusco that Azarello had flipped on him and told IAB of the murders he had committed for Stills. He also told Fusco that they have information on where Fusco buried Stills body. But Carter with help of Bear removed the body and when Soriano got to the site he found the ground dug up with no body. Enraged Soriano accused Fusco of killing Stills and promised to hang it on him. Fusco told him that he's wrong and walked away. His investigation is ended fully when Finch gets Elias to "convince" Azarello to recant his confession. (“In Extremis”)