State police are trying to determine if an off-duty sergeant was drinking prior to a September crash.

Police are investigating if Sgt. John McDonald was drinking at a retirement party for a fellow trooper before getting behind the wheel of his unmarked state vehicle.

McDonald is accused of striking a car carrying a Southbury woman and her teenage daughter. Lisa and Madison Conroy were headed back from a mother-daughter outing to get ice cream. Instead, they ended up in the hospital.

The crash happened on Sept. 25 on Route 188 near Airport Road in Southbury.

A police report shows that's when McDonald blew through a stop sign at the intersection and into the Conroys. The impact caused both cars to go off the road and into the woods.

Police say McDonald had just come from the Black Hog Brewing Company in Oxford.

He and the Conroys were all injured and because of that, no field sobriety tests were performed.

"Generally medical treatment outweighs a field sobriety test," said the state police commissioner's assistant Brian Foley.

Foley says what happened at the hospital isn't known but it appears staff didn't draw blood to check if McDonald had been drinking.

"It's a great concern to the commissioner and the colonel of the Connecticut State Police. With that, this is a three-layered investigation -- motor vehicle accident itself, criminal investigation based on the possibility of DUI as well as an overlapping internal affairs investigation," Foley said.

An attorney for the Conroys plans to file a lawsuit shortly.

The father and husband of the victims, Kevin Conroy, said "I'm very thankful that I'm in attendance for this meeting here to discuss what's going on versus planning or attending a funeral."

McDonald has been a state trooper for 13 years and is with the Western District Crime Squad. Foley says McDonald took a few days off due to his injuries and is now back at work, pending the outcome of this investigation.