Who killed Wellington ?

There are currently many theories as to who killed Mrs. Shears' dog. The main emphasis is that it must be a character that nobody would suspect. On purpose, or by accident?  I'd say it was Christopher's dad.

Wellington used to be Mr. Shears' dog; and Mr. Boone had told Chris not to mention his name in the house, because he hates him so much. Also, Mrs. Shears wanted to live alone with her dog, and Christopher's dad must have killed it because he thought she would then move in with him and Chris. These theories show, the dog must have been killed through the anger of Chris's dad. 

There is a chance that Mr. Boone did not kill Wellington, because there is no exceptionally strong motive as to why he did. Also, Christopher's dad would seem like he isn't that type of person because he's so calm with Chris; unlike his mother. There is a part in the book explaining how he is drinking on the couch to maybe help ease the pain inside him. This unlikely incident may have occurred without him even thinking about it. Yet would he really want to hurt Mrs. Shears like that? 

Mr. Boone has many sides. Including anger and compassion; (as we have seen in many of his interactions with Chris). The dog must have attacked him first because he is at Mrs. Shears house a lot; and it must think of him as an intruder. She could have made her dog attack Christopher's dad because they may have been in a huge fight at the time. Either way, if he killed the dog with a garden tool, he could have easily placed it back into her shed becuase he has the keys; since they always do favours for eachother.

Chris's dad killed the dog out of his rage towards the many people in his life that have took advantage of him. If his wife never left, he would have never had all that anger inside him; and he wouldn't have know Mrs. Shears that well- which would never have brought up that motive.