I found a dead squirrel in my garden today, a fully grown, lactating female. She had no marks on her at all, and was well nourished and of a good weight. Her fur was glossy and thick, and apart from the fact that she was dead she looked perfectly healthy.
Very rarely a squirrel may sustain injuries - or even die - from a fall, but usually from a height of at least 30ft. This one was underneath a shrub as tall as a person, and a six-foot garden fence.
Could she have been poisoned? If so, I consider myself very lucky to have found her before my dog did.