Any ideas what may have killed two little squabs?

Hi,

Unfortunately I found two dead baby wood pigeons on the lawn today below a conifer tree at the end of my garden. It was very sad as the two parents have been daily visitors for years and we are very fond of them. Thankfully the mother appears to be unharmed as we saw the parents together again this evening - needless to say they got extra food tonight! 

Just wondering what people thought might have happened to their Squabs? I was out in the garden at lunchtime under the tree and there was nothing, I found them dead at about 5pm, so it had to be this afternoon.

They had clearly been attacked, but I thought it was odd how they had been left on the lawn together. Why would they not have been taken for food? They were about the size of a fist, so too young to have fled the nest I think(?). 

We do get a lot of Magpies and Crows around us as there is a woodland close to our house. Occasionally birds of prey - but not often. Could another bird have attacked the Squabs? However, when we leave food out it's normally the Wood Pigeons bullying the Magpies!! 

It has been windy lately, but relatively calm today and no evidence of a nest fallen out of a tree. 

We do have a cat next door, but they hardly ever come in the garden and we've never had any dead birds, despite daily feeding for years. 

If anyone has any ideas then I'd be interested to know.