It is unlikely that it killed the angel all at once. Did you see marks from a beating? Did you see it beat the angel? If not, then it is not likely that it killed it... most of the time it takes days for this to happen, especially since they got along for so long.
If the angel survive tonight. Try this.
- Download picture of coral beauty from internet.
- Print out the 6-7 pictures of the coral beauty angel in COLOR
- Cut it and post it on outside the tank.
This is may sound crazy but it work for me. Every time I have fish that picking on the other, I use this method.
Sorry about the angel.:sad1: