One of my neons died in just 4 days?

i got fish last sunday i got 2 male long tailed guppies and 2 neons. one of the neons dies like 4 days l8er after i got her because the tale was gone oen fo them must of attack her and got the tale off. but the question i wanna no is which fish did it one of the guppies or the other neon. would the neon tale grow back if it was half of the tail? i took her out of the tank for the nite to avoid any further damage but she died and i flushed her down the toilet. would she of survived if it was only half of the tail or died anyway. which fish do u think would of done it? o and here's the fish by the way and yes this is me talking feel free to comment if u like
http://www.youtube.com/watch?v=d_4ydxeoi...
Answers:
Most likely one of your guppies bit your Neon because Neons are community fish and rarely are aggressive. And your neon probably would of died from Tail Rot soon after unless you treated the tank with Tetracycline. But since it's such a small fish there more susceptible to infection and disease. You did the best you could do in such a short amount of time, I reccomend watching your fish's behavior much more closely, especially your guppies and separate the aggressive ones.
I hope you'll have better luck with your fish!