We put down a beloved pet this past summer, an English Pointer, who for unknown reasons had gone psychotic. It was a matter of public and personal safety.
He attacked neighbors, neighborhood kids, mauled the dogs of neighbors, and then he turned on us.
Could have been a brain tumor, could have been due to a stroke; whatever the reason it was very sad. He was only five years old.
My condolences.
However, you did the right thing. It’s not worth the risk that he could have eventually killed or seriously maimed someone.