I think (and hope) I saved somebody's life today

I was traveling through town with my 2 kids, it was a misty rain coming down. I was northbound on main st and the vehicle ahead of me was traveling at a low rate of speed maybe 15-20 mph. Coming to the light at Madison Avenue the light turned yellow and the vehicle ahead of me stopped almost a car length into the intersection. i was stopped at the white line and was wondering what this dude was doing. Vehicle proceeds to take a left on Madison Ave traveling in the parking lane of all places. stays in this lane for a few block and then veers over into oncoming lane. Good thing there wasn't any traffic coming at him. Speeds went from 8mph to 35mph . He turned into the Health Club lot and turned around. I have since called the police and reported this guy. After his turn around at the Health Club he absolutely flew back into town. I kept an eye on as he got caught at the light and I caught him then. While traveling down Robert street south, I noticed an officer that started to come out to monitor him. I slowed down at the light in the left lane to turn off. While turning off to the left and having the officer behind the guy the vehicle in question came into my lane and almost hit me. I sure hope the police saw that!! I have no tolerance for drunk drivers. If this guy was drinking and driving and would have hit somebody and I didn't call him in could I have lived with that?