When I first watched this episode I was not sure why Gus brutally murdered Victor. Now I think I understand. Victor was seen at the crime scene of Gail's murder. If he was ever identified, the police would have to investigate him, and this could potentially lead back to Gus. So Gus killed him to prevent this from happening. Killing him it in front of Walt, Jesse and Mike also served as a very effective intimidation tactic. I really love this show, it deserves all of the hype surrounding it.