Random NEW dead mice found outside house?

I was walking to my backyard (all concrete, no place for burrows) to spraypaint something, and noticed a brand new dead mouse by the stairs leading down to my yard. Thinking this was just a random pest, I discarded it. I had to get a diferent color spraypaint, and on the path back (I JUST walked down it, 10 min ago to get to the yard) there was ANOTHER mouse. I am almost CERTAIN that it was not there before, since I distinctly remember looking at that exact spot when I was walking down, because there was water there, and nowhere else. This mouse was also, BRAND NEW. It couldn't have been dead for more than 3 hours.

I don't have mice in my apartment. I have no traces of mice in my apartment. Nothing is ever chewed up, there are never droppings, fur, etc. I never hear noises at night in the dark.

The curious thing, is that my neighbors have these bags tied up to their railing, which is quite close to my walkway and porch, and they're filled with something. It looked like dog poop, but I don't know why they'd have dog poop tied up to their railing, but there are multiple bags, knotted tied on the ground attached to the railing. Could this be mouse poisoning and the mice are coming out NOW and eating it and dying on my walkway and backyard?

This is really weird, and disgusting, and I don't want a new mouse infestation so I'd like to know if any of you can offer advice.