Canary killed by finches?

I have a mixed aviary of 3 Society Finches, 3 Zebra Finches, 1 male Canary, & 1 female Diamond Dove. This morning I found my canary dead in the seed cup at the bottom of the cage. These guys have been living together very peacefully for a year and "Tweety" was singing and acting fine yesterday. My Zebras & Societies both had eggs in their nests and I had noticed the male Zebra harring everyone in the cage since the eggs were laid. However, I didn't think he was a danger to the larger birds (Canary & Dove). The Zebra's nest was on the ground this morning and the eggs were broken and on the floor of the cage as well. My question is, since it happened overnight and I only found him this morning. Do you think that the the male Zebra actually did kill my Canary, or that it was some outside influence (such as my cat somehow getting his claws through the cage bars and getting really lucky to snag Tweety)?