The case has pitted officers against the families of two men shot dead by Ontario's provincial police in separate incidents in 2009.
The families argued before the Supreme Court that having a lawyer approve the notes that end up in their memo books is unacceptable.
They also said that allowing a single lawyer to act for several officers involved in an incident undermines rules against collusion.
Police argued they have the right to talk to a lawyer of their choosing before finalizing their notes.
In November 2011, Ontario's top court sided with the families.