If I were a cop I wouldn't have much interest in talking to a suspect, unless his accuser was suspect. A guilty party is just going to snowball you with misinformation. But then I'm not a cop. Perhaps talking to all parties as a matter of course would be the best practice.
Medical records are evidence. If they didn't have ANY evidence the man would get off free. That's why the crime rate in the world is so high. Everyone knows that if they don't get caught they will get off scot free. That's why about 75% of crimes go unsolved. It's just the way this messed up world is.
Medical records and testimonies are evidence, usually the only kind they have when there are no witnesses. Yes, they interrog--I mean, question-- 'the guy' regardless of whether you're referring to the victim or the perpetrator here.
you need medical records and photos of the damage (any bruises or cuts, etc.) how long ago was the assault? because it needed to be reported right away, within hours of it happening. it's not something you dwell on a for a while and then decide that you want to press charges.