Bullfrog threat to pond fish?

Question:

Just wanted to know if a large frog (bullfrog) would kill all my fish in our pond. It’s a good size pond with Koi and others, lots of lillies and grasses too. A friend said the bull frog would kill my fish. I have about 12 fish3 large Koi and the rest smaller. My pond is about 5 years old and is doing wonderful. thanks Patti ivie