[Highland Park] roaming aggressive dog

At 4:00 in the afternoon on Monday June 8th, a white and tan muscular dog with purple color with no identification was roaming N. Sheridan Avenue between Grafton Ave and the Park. We saw it attack on two separate occasions dogs being walked. This frightened both dogs and owners.When the other dogs were gone, we got the dog on a leash and it was not aggressive to the people with him. Our vet suggested that we bring the dog to them to be scanned for a chip. The dog is on his way to the vet now (4:30). We will keep you posted as to what happens with the dog. If you know anything about this dog please contact Rick Rogow at 412 648-7319