This is terrible, the poor dog; his owner let him down big time. If she'd bothered to treat him properly - train him, keep him in, muzzle him when out - this would never have happened. She is a fool and shouldn't be allowed to own another dog.
To all those people who are dubious about the complaints made to the police: I can very easily believe they turned a blind to his other attacks. A family a couple of doors away from me have three very large dogs (Anatolian shepherd, Neapolitan mastiff x lab and something they call a Japanese mastiff), the latter has made numerous attacks on other dogs, and one on a woman when it couldn't get to her dog. All these attacks have been reported to the police, we (the neighbours) have also reported them, for letting their 12 year old walk this dog. Nothing has been done about it.
Also, with such powerful dogs it really isn't that easy to stop them once they start to attack. They aren't like other large breeds. On one occasion this dog attacked a collie outside my house, my DH, my BIL (both big powerful men) and the owner of the collie couldn't stop it. At one point, my BIL kicked it hard in the testicles - it turned, snarled at him then continued to savage the other dog. Finally, a van full of builders pulled up and one jumped out with a rope, and very nearly throttled the dog before it let go. Meanwhile, the owner was doing nothing more than telling it to be a good boy and behave itself.
I love dogs. But if that thing got hold of mine, I'm afraid I would do whatever it took to save him.