Here in the US that means "lawyering up instead of being dumb and running his mouth", not sure if it's the same over there. If he was really not cooperative the police would be more than happy to say exactly what (they say) he did.
It's just the smallest, easiest to prove thing that allows them to lock him up for a short time while the investigation is getting started. When they know more about what actually happened they can file more detailed charges.
Strong privacy laws prevent them from doing that. I saw an interview with a police officer and they could basically not say anything at all. Most info comes from journalists.
Here in the US that means "lawyering up instead of being dumb and running his mouth", not sure if it's the same over there. If he was really not cooperative the police would be more than happy to say exactly what (they say) he did.