It may be that the police will come and ask you if you saw anything or it may be in the local press.
I remember coming home one night and the ginnel down the side of the park I lived on was sealed off, as was the whole park, with police , dogs and forensics everywhere.
I had to sign in and out for a week but at first, the police would only give very limited information, just that there had been a nasty assault at first.
I was worried sick as I was looking after 4 houses and about 13 tenants and managed to track down all but one and it took us a while to get hold of her.
We only found out the details (nutter with two knives stabbed a woman 7 times) when the police started doing doing interviews but moreso when it was in the local press.