Is tiger barb really that aggreesive? I was so shock that I lost 5 neon tetras overnight that time. I have seen one of the cardinal after eaten but most of them (and all of the neon) were simply disappeared without a trace.
I have never had any of my tiger barbs kill any other fish, although they are kept with 14 other golden and cherry barbs, the only other fish in the tank are bottom feedes (plecos and corys). When they get bored however they do chase my cat fish back into his clay pots, and if he trys to hide in the plants they nip at his fins. I spoil all my barbs and I am pretty sure if I tried to introduce some neons into the tank that they would have there way with them.. but who knows. In your case I cant really see what else would be doing or causing this.
I hope you can come to the bottom of this, but from what I can see its your lovely tiger barbs