yeah you could of stopped it...
To respond to if feeding live fish makes them more agressive, maybe. I have fed my RTC only pellets, bloodworms, and beef heart. So far he has not attacked any tankmates, which are; 2 9 inch phantom knife fish, 2 xray tetra, 2 glass fish 2 neon tetra and 3 scissor fish. So far he hasnt been agressive let-alone eat one of them. But more then his diet being live or not I BELIEVE IT IS THE TANK SET-UP THAT IS MOST INPORTANT. I like the realistic look so i made him a HUGE cave out of slate 18x18 and put a nice peice of driftwood which give the smaller fish a place to dash and hide. Having them in an open tanks makes them more agressive and aggitiated. Giving that he spends 99% of the day sleeping in it, I couldnt imagine him every being agressive or a danger to other fish in the tank.