Dead Baby Rabbit

OK, so I was at my grandparent's house playing in the backyard, when I found a small baby bunny. It was very clearly dead, it was on it's side, eyes closed. My younger cousins were freaking out, so my grandma came out and picked it up with an inside out plastic snack bag. (Like you would with dog poop) After I took a few pictures for science purposes, she threw it away.

At the time, I estimated it was too young to be out of the nest. But after some research, it turns out it might have been 2-4 weeks old, meaning depending on how old it was, it could have been off on it's own. Apparently Cottontail Rabbits are almost completely on their own at 3 to 4 weeks.

It's eyes were closed, but I think that was just because it was dead. It didn't have any marks that indicated it was dead. It's feet were a little damp, but I'm pretty sure that's just from the dew. There were no predatory marks, and I took a few pictures because I was curious.

It was under a tree, the whole yard was well fenced in, and there were a few holes around the yard.

A few weeks before, my little brother and I had noticed a Cottontail Rabbit in the yard. We had dubbed it Nubbles, and I think Nubbles is a mother!

My guess as to how the rabbit died is that it was it's first night out of the burrow, and it froze to death. It's still having pretty frigid under freezing nights here, so it isn't out of the question in my opinion. There's honestly no concern or hurry, I'm just genuinely curious. There's plenty of places of people talking about skinned, beheaded, or disemboweled rabbits, but none about young rabbits without any marks. Any answers?

If this matters any, I'm in the suburbs of Chicago.