Makes me sick to think of this, but, how did he get her into that without, um, doing something to cause her body to fit inside and close the lid?
In the Jodi Arias case, a member that I cannot remember their name, did some examples and taped it with photos, videos... and shared it with us as to show how something could have been done.
Just now, I went into my garage and found and emptied a 92 quart (23 gallons approx) sterilite container. I squatted down in the container and I could have been in it with just four inhes of clearance, but I am 5'7" and 155 lbs. (Don'tjudge!). That is much bigger than she was. I think she would have fit into this is it was before rigor mortis took over.
I don't have somebody else right now to take a photograph of it, but 92Q is about 23 gallons. And they were very popular around Christmas time.
Attached is a screenshot the sterilite container, this one does not have me squatting in it but somebody else can have their significant other take a photograph of something like that. If they would like.
The width of my body fit very easily.
ETA
Oh, and I just did it again and I think I probably could scooch in and fit in completely with the lid it came with.
ETA to do this picture, I had to take out Christmas stuff. So very interesting, that the mother said she was getting ready for Christmas but had not bought a tree. Could the container have come from her house, or his, that had Christmas decorations in it that she/he had taken down and he just use that for the disposal. I guess not because it was said to be a thick black plastic container. But it just made me cringe when I just thought of that.