Ontario's highest court says police officers under investigation by a civilian watchdog can't get a lawyer to help them prepare their notes.

Tuesday's ruling by the Court of Appeal for Ontario is seen as a major victory for the families of two men shot dead by police.

Ontario Provincial Police officers shot and killed 59-year-old Doug Minty and 30-year-old Levi Schaeffer in separate incidents in June 2009.

The families had lost an earlier bid to get the courts to intervene in how officers deal with their notes.

The families contended the officers involved in the killings had violated laws on how police co-operate with Ontario's Special Investigations Unit.

The SIU investigates incidents involving police where there has been death, injury or allegations of sexual assault.

The Court of Appeal ruled police officers can get legal advice on the nature of their rights and duties, but not to vet their notes.

Lawyer Julian Falconer represented the families and calls the ruling a huge step forward in the battle against police manipulation of SIU investigations.