Fledgling Rook died, what happened?

Hello I am new to this forum and to birdwatching.

Five days ago, we found a fledgling Rook in our garden. We do have a lot of Rooks around as we are surrounded by big trees. At first we thought it was injured but then watched it and it was hopping around, so we assumed it was a fledgling. We have a dog, so we put the fledgling on our shed roof in the hope it’s parents would do something however it fell off the roof! Our dog has free rein in our garden as he’s small and uses a door flap, however we were worried about the rook so we put him on a lead to take him out. Every time we went outside what I assume were the Rook’s parents would screech and circle overhead and the fledgling would seek cover in bushes. I kept googling for information and we put some food out for it as the parents did not seem to be feeding it. Yesterday morning, my daughter went out to see how the bird was doing as we had started to see it as our little pet and unfortunately it died sitting in the last place we saw it last night. I was cold and wet last night and it hadn’t sought any cover. We are going to bury it, but we are confused about why it died and whether we did something wrong. Can anyone help?