So sad for your loss 
Very sad though that you are torturing yourself this way. There must be millions of 'bin incidents' with ddogs! Short of hanging a bin off the ceiling it seems ones that extremely difficult to avoid 
Every now and again something 'freak' happens and a ddog gets unlucky. That was your boy sadly. Horrible things happen and if we stopped everything that's any risk we probably wouldn't even have ddogs atall.
You haven't done anything with intentional harm.
In our garden recently I had left the garden to go into the drive via one of the back gates.
I found my ddogs wandering along the road!
I have since discovered a weird thing has started happening with the latch, but that could have been a multi accident rta of appalling proportions, involving more than ddog and car/s
I couldn't have known about the latch being weird, I've put other measures in place now, but it might've been too late.
I also have bins that they could access, as do all, and unless veggie, they'd all have bones in.
Please no more beating yourself up over this.
It's part of grief to go through a guilt phase, or the if only, but its one that can make grief get stuck so you can't move on.
Your ddog knew you adored him, you can't do more. I'm so sorry this freak incident to him away from you, you did everything in your power to make it alright for him. Sadly sometimes there isn't enough we can do.
They live such a big hole in our hearts 