The gun was to control Travis. The knife was make to make it real personal. I've noticed a lot of blood spatter on the outside lip of the shower. It wasn't disturbed by her putting him back in the shower. So, I'm trying to figure out when it would of got there. Like the blood on the baseboards of the potty room. Travis would of been down ,not standing when it got there.
The knife was used to kill Travis Alexander, a lot.
However, the rationale for the gun is like a Rorschach test for people, based on what their theory of the crime was.
Really, the gun is tiny, not at all visually imposing and could be mistaken for a toy. Although the gun could do damage, and easily kill, as far as being the sort of thing one would brandish, I don't accept that out of hand, then again, it's just psychologizing on my part too.
Personally, I think Jodi Arias brought the gun out of the old adage "better to have one and not need it, than need one and not have it". Its purpose was to make sure Travis, maybe Mimi Hall or whatever unfortunate witnesses were around weren't for long, to that, I stick by the idea that Jodi Arias appeared on the scene far later than she claimed, making sure Travis was the only one in the house, up to and including lying in wait in her rental car. What's the point of all the stealthy premeditation if somone saw her there and lived?
Assuming Jodi Arias' premeditation was structured, my sense of the purpose of the gun, and the rationale for bringing it is the above, and also that being a person who seems to have formed a lot of her ideas from movies, the .25 was for the coup de grace, a shot in the head to make sure Travis Alexander was dead.
If not that, then I will remind people that someone with their throat cut doesn't die quickly or easily. Even when they lose consciousness, gurgling, gasping, choking agonizing reflexive breathing can go on for minutes. Even if Jodi Arias didn't plan on using the gun, the not-so-quick-and-easy nature of actually killing someone: Slashing, stabbing and throat slitting would have made her resort to it.
You know, deaths in movies are kind of easy. So much so I wonder if they actually trivialize murder by making it all seem far more merciful than it is. People get shot and fall down dead, strangling someone takes 30 seconds, the near-death drowning in The Abyss takes no time at all and the long protracted explanation of the physiology of it in Sebastian Junger's Perfect Storm, which will make you not want to take a bath ever again, is treated with a painless cut-away in the film, etc, etc. The only film I can think of offhand that makes a point of how long and protracted killing someone is would be the infamous Gromek killing in Alfred Hitchcock's Torn Curtain.