well ur case is making no sense. He gives you a death threat in front of witnesses (otehr cops) and YOU get suspended? We have cops here put peoples heads through windows and dno't get suspended. And no one ever gets a chance to talk to the chief. It always go through IA. Cops get complaints ALL THE TIME. In fact during the initial hearing, there is NO ONE allowed except investigaotr, officer being investigated and a camera (and shop steward if allowed). You should talk to the attorney from your union.
Union and state rules may be broken here. Look up garrity rights. And no matter the ruling - you can always contest it. Complaints about beat cops are a dime a dozen. IA is *usually* on your side and just want to finish the paperwork and move on.
You should post this on officer.com.