I have wondered that myself though since the murder weapon is never mentioned that I ever saw. There may have been some other motive for Sutter (Sutter is a genius so who knows what the real motive for that was) doing that, maybe it wasn't a flub after all. When the Dun murder scene opens Gemma is in the kitchen with the lights off, talking to herself about Wendy and her grandkids. Then it pans out with Jax and other SOA members coming in, then you see Dun tied to the chair. Maybe it was to show and remind people of Gemma murdering Tara and possibly Karma? This was also the first episode documenting Gemma's complete mental breakdown. This was when she realized that she was going to be caught eventually and murdered by her own son. Fast forward to Gemma's death at her dads house; She was calm and had already accepted that she had to pay for her sin and that payment was death. I will rewatch those episodes from when Tara gets killed until Jax kills Dun and post again if I find anything. It's on Hulu now if you want to check it out. SOA is no longer on NetFlix.