The Sun headline is overstated. Read the article. Nowhere does Dog say Brian killed Gabby while calming her down. This is a sensationalized interpretation of what Dog said about the Moab DV incident:
I know that she was very verbal because as they were arguing one time, the vacationers around them heard her yelling,” Dog said. “I know that he calmed her down usually by grabbing her mouth like that.”
The Sun took this statement and twisted it to make it appear Dog was speaking about Gabby's murder when he was actually speaking about the Moab incident. I am a little hesitant to defend Dog (I've never heard of him before this case) because he does seem to be a rather outlandish character, but I get disgusted at the news media and their tricks to create controversy and sell more papers.