"No doubt Diogenes is there, and no doubt Mr. Toots has reason to observe him, for he comes straightway at Mr. Toots's legs, and tumbles over himself in the desperation with which he makes at him, like a very dog of Montargis. But he is checked by his sweet mistress."
Here is a URL to a French tale of a dog who identified and
convicted his ownner's murderer:
http://www.adopt-a-greyhound.org/atail/body_montargis.html