I doubt it was killed from fighting. of course, I do not have much to go on to make such a silly remark, but that has not stopped me before.
Let me explain. A healthy monitor, does not die easily. If it was from fighting, there would be blood and parts all over the cage, smeared over the entire battle field.
Its also very common for cagemates to attempt to consume their dead brothers, or finish them off, then consume them(afterall their dead, why let it go to waste). Natures way I guess. I actually did some experiments on this. More of my bonding behavior stuff.
So, from what you said, "some blood" it would not indicate murder, murder is messy.
On the otherhand, constant bickering causes internal stress, which allows lots of problems like organ failure.
The problem is, its so very hard to diagnose these things for one reason, monitors(and specially ackies) are so very strong, they do not express symtoms until its to late(advanced symtoms).
Of course, if you have a keen eye and lots of behavioral experience, you can see these things well in advance. But the problem is experience. Its gained from lots of events like yours. I believe its called painful experience, learning from the negative. Thats how you get to be an expert with monitors.(learning from mistakes)(on a daily basis) hahahahahahahahaha i could go on.
Pics would help, here, but I do not think a Vet will be of any help. Save your Vet money for a sick monitor, not a dead one. Sorry for your loss