Good neighborhood/trashy neighbor

We bought our house exactly a year ago. It’s a great neighborhood, however, there is one multifamily thats rented out to really trashy people.

Yesterday, there was a man and a woman fight on the street and they threw a knife that ended up on my front yard almost on my feet. My son watched what was Happening and was so frightened. The woman was screaming so much so I called the police. When the police came, the basically lied about everything and said that nothing had Happened. When those people saw me they yelled at me and warned that I should mind my own business.

I’m not really sure what to do... I feel threatened and I don’t know what I can do about it! Any suggestions?