Violence on the lawn

We have been enjoying watching the Moorhens out on the lawn over the last couple of weeks with various combinations of adults, juveniles and new chicks. This picture was taken a couple of days ago. We were watching one of the juveniles this afternoon in charge of three chicks today when tragedy struck - or at least we are pretty sure it struck. The weird thing was that we were just discussing the vulnerability of the chicks as they became more separated on the lawn. I had just finished saying that I thought the only response of the juvenile if danger threatened would be flight rather than fight. We were thinking of cats really. Suddenly the juvenile, followed immediately be the chicks, ran for its life. Swooping down at high speed was a bird of prey and it seemed to reach the moorhen family right on the banks of the moat. I assume it got one of the birds but I was already heading downstairs and out the back door so I didn't see the bird take off again.
I wasn't sure whether the bird was a buzzard or a sparrowhawk or indeed something else but it came down at high speed. If pressed I would say it was a buzzard. It was a traumatic and brutal moment and although it is perfectly natural it was also upsetting.