I have had a very fat pigeon sitting outside my living room window every day for many months. Very tame and likes to visit the bird bath for a drink and a wee splash around. Also followed me when I was digging. Today there is just feathers scattered over the garden and no sign of Archie. I fear the worst and can only hope his end was swift and painless.
How lovely to have an Archie in your life....I suspect he felt similarly about you and that he died happy......and that is always a blessing. I hope you are found by another Archie who needs some kindness and company.
I did think of a sparrowhawk too. Saw one take a pigeon a few years ago and it was so fast it was just a blur. Ah well, think Archie had a good life and maybe son of Archie is around somewhere.
I saw a sparrowhawk take a pigeon that was sitting on our garden fence. The hawk came down behind the bird and carried it down to the ground. I reckon that the bird was dead before it hit the ground. The hawk took about 20 - 30 minutes to eat the head, neck, and breast.
Sparrowhawks have realised that our gardens provide much easier pickings than the countryside. And, judging by your description of the pigeon, maggie, i would think the sparrowhawk to have been a female as males normally go for smaller prey.
It's my guess that, the pigeon was swooped apron by a sparrowhawk, took what wanted, breast maybe, then a fox came along and took away the rest of it.
An old bird like that is easy prey for a bird of prey.
When Queen Victoria visited the Crystal Palace for the Great Exhibition in 1851 in the company of the Duke of Wellington, she complained about the mess created by pigeons and asked what could be done about it.