What does a police certified case report contain

I was arrested for domestic violence two years ago but no charges were filed against me but I was asked by IO during an interview for my I485 application to submit a certified letter saying that no charges were made for that arrest. I went to the local PD and they said they will only send the case report directly to USCIS. Now I am afraid what such case reports contain. Does anyone have ever seen a police case report or know what kind of information it contains?