Why was he still driving...
This story may help explain some of the reason:
http://www.indystar.com/article/20130428/NEWS/304280032/David-Bisard-kept-driver-s-license-because-legal-quirk-earlier-case?nclick_check=1This link makes the point of saying in Indiana that law enforcement need probable cause before a blood test can be drawn. looks like that may have not been done in the first case according to the judge. The title in the first story also says "accused" not "convicted" so maybe in the first accident the officer may not have been found guilty yet? The first story mentions he is suspended from department not fired so that looks like they would wait for a conviction to fire him too. I guess one of the cases where innocent until proven guilty can bite society in the butt.
To get long term punishment on DUI cases can be hard to do since many judges and juries have driven drunk in their lives and they can sometimes look at the suspect as a good old boy who made a mistake like them and just had bad luck so they want to cut an average Joe some slack. Otherwise you could have stiff penalties and cut out loopholes in the law. Look at the homicide laws....if you killed someone with a gun or knife you would serve years in custody, yet kill someone while DUI and you serve very little time.