Why wasn’t he arrested that night?

My friends encores me over for a night of drinking in which after we were to take our cats to get fixed at the vet the next morning after a misunderstanding with how he perceived me handling his dog he assaulted me tried to kill me breaking my back in three places I had to run for my life for a mile down the highway until a bystander called 911 where I was transported to the hospital to assess my injuries the cop said I could file a report but he didn’t even investigate my assailant. He did nothing why? The cops didn’t seem to believe he was seriously threatening my life there was only a note that the report had down that they told me to go to the magistrate but he threatened to kill me if I went to the cops so why didn’t they arrest him?