My first suggestion would be the Opaline Gourami. This is the species Trichopodus trichopterus, which is available in several varieties but all are the same species and it is one of the most aggressive of the small/medium gourami. If you happen tohave a male, he will consider the tank "his" in the same way male cichlids (like the angelfish) do, and this gourami has been know to kill every other fish in the tank. Even females can behave accordingly.
Gourami and cichlids should never be combined so I would remove the Opaline and see if this solves things.
It is possible that the bichir is responsible, though perhaps less likely. This fish will certainly eat small fish, but whether it takes on larger I cannot say with any certainty.
The angels themselves are also possible, but with this fish they generally "fight" until the less dominant is dead, and you would see evidence of this interaction most of the time.
