The timeline is grossly off here. I know. I knew both officers personally and was a Town official at the time.
The robbery in Nanuet took place just before noon. Officers Brown and O'Grady, along with officer Keenan, who survived, were gunned down stopping the getaway van entering the NYS Thruway in Central Nyack. In fact, my father, who worked halfway between Nanuet and Nyack was driving home for lunch as he always did. I called him from Town Hall to ask him to go give blood at Nyack Hospital and he he asked me if it was for the "traffic accident" in Central Nyack.
The Town Supervisor dispatched me to Nyack Village Hall to see what assitance the Town could offer. I can remeber talking to the Mayor and saying to him that it sounded something like the Weathermen would do when I was in college.
Wow! Thanks for the firsthand account. believe it or not, I posted my previous before seeing your post.