Is it morally okay to unchain someone's dog?

There is this dog near my grandma's house that has been locked in a box not longer or wider than 1 meter. He's been locked there for at least 10 years, during which I've never seen him out. I started thinking that I should go there one night and open his cage and let him out of the yard. I would try to... show more There is this dog near my grandma's house that has been locked in a box not longer or wider than 1 meter. He's been locked there for at least 10 years, during which I've never seen him out. I started thinking that I should go there one night and open his cage and let him out of the yard. I would try to put him on leash and take him downtown where there is more people, food and some strays. I wouldn't be able to keep him as I already have a lot of animals, and I'm not even sure that he would allow me to leash him as he always barks whenever he sees someone. Would this be a mistake? Would I make his life more miserable by letting him out or leaving him there? Should I do it? I feel no remorse for the owners, they can't love him and keep him like that for 10 years.
Btw where I live there aren't any animal rescue institutions, so it's not an option calling anyone.
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