Tara's, Edalene's, and (possibly) Arbenia's deaths are because of District Fourteen....along with half of the tributes in the 405th Games. Clearly the Capitol and District Fourteen are using ninja spies to annihilate the ninja spies of the others. Tara was pro-District Fourteen, as was Namitha, hence "Welcome to the Games". It was a warning sign for Namitha not to get involved. Edalene was the same way, but she was taken out by the snipers of the Capitol, not because she revealed too much (well, that too), but because there was a high risk of her or Namitha figuring it out. In contrast, Arsin is a warrior of the Capitol, and thus District Fourteen (might have) killed his girlfriend to rattle him so he wouldn't kill their allies in the Games (or win the Games). Note how he leads the Careers (mostly pro-Capitol) in taking out The Alliance of the Mockingjays? Revenge. Unfortunately, Namitha survives, but a fair amount of pro- D14 fighters were taken out. Also, Kildaire and Kyler are on one side and Charity is on another, probably pro-Capitol, with the Careers, hence the betrayal. Kizzy is honestly neutral. Tod doesn't care who wins as long as everybody dies.