
Continuity mistake: When Gus walks towards the nursing home towards the end of the episode, two flags in the background stop waving, but in the next shot they suddenly wave again.

Visible crew/equipment: When Combo is watching a black car parked in front of him while he was dealing as the episode started (a few moments before he's killed), a stage light can be seen reflected in his sunglasses.
Chosen answer: There are several possibilities. Gus primarily does it to make an example out of Victor. Victor is one of Gus' most loyal henchman, and yet he had no problem killing him. Meaning it doesn't matter how loyal or valuable Walt is, he can still be killed and it won't bother Gus. However, Walt tells Jesse that perhaps Victor "flew too close to the sun." Meaning, Victor over stepped his bounds by learning how to cook meth. Gus didn't appreciate Victor's initiative and Gus only wants his employees to do the job they're given. Again, telling Walt and Jesse to do their job or else.
Bishop73
I think it was a combination of anger over Gayle's death and Victor being seen by witnesses makes Victor very vulnerable and therefore a dangerous liability to Fringe's empire.
By this point, the mugshot of Victor will have been spread around as a suspect in Gail's death. Victor had been come too hot to handle, so to say, so had to go.
Ssiscool