Apparently the police can only arrest people when they have specific evidence of an actual crime being committed. I reported some obvious drug activity in a neighborhood where a close relative lives. There were people coming on foot to buy drugs a certain apartment every few minutes at all hours. But the police did nothing. I imagine this was because:
1. The actual sales were taking place indoors, making it difficult for them to observe a crime.
2. There were many other places where drugs were being sold.