Paquette: What kind of gun did he have?
Costa: He had the kind that leaves really big holes in people.
Costa: Come on, Illeana, you didn't fall for James Costa. Someone as beautiful and powerful as you doesn't fall for a faggy art dealer. Okay?
Martin Asher: That guy was nothing, all right? I didn't take his life, I lived it. I was the best thing that ever happened to that guy. You looked at him, and you saw me, and I looked at you, and I saw you, and we are the same.
Answer: As "Costa" was initially a suspect, the police took a DNA sample, which did not match any DNA on file - that was what they meant by "he's clean." It basically means that Asher was very careful at not leaving DNA evidence (other than that of others like Hart to frame them). Presumably the real Costa had no DNA profile linked to his identity on file either, or it could have returned a mismatch and revealed Asher's deception.
Sierra1 ★