Do I report my neighbour's aggressive dog?

For the third time, I saw this dog (pitbull) harass others, and it was never on leash. When it frightened my little dog, who was on lead, I scooped him up for safety. The owner just smiled and suggested that I should have let them sort it out themselves. I've reported the dog to the council, and the officer now wants me to record a statement. I socialize with these people, and they would know that it's me. So, should I make it an official complaint, which could lead to a fine, or just leave at the level of a council "warning"?