Because the drugs are controlled substances - and because they ca be used with the spring-loaded guns to kill people.
No, the cops weren't already there - they were sent in response to the 911 call. A few paramedics arrived first but refused to go in because the tiger was still loose. Some of them did, though, and the rest went in after the cops arrived and one shot the tiger.
There seems to be a considerable amount of confusion around concerning this whole event. And part of that is due to new information becoming available. Apparently, some folks read the original reports and haven't bothered to keep up with the story since then. And I don't mean you, just talking about the public in general. It just seems that once some folks hear the initial news they form their opinion based on what was said then - and that's the end of it for them.
The 3 men had been drinking and were shooting the tiger with stones using slingshots. The slingshots were wrist-rockets, which are high velocity and considered a weapon in NY. Imagine all 3 of them nailing the tiger at once.
The tiger jumped/clawed its way up the wall and got them.
These drunk men then ran around yelling that a tiger was out. No one believed them. They didn't see a tiger because it was busy killing one of them. Then it went to the cafe, where it attacked another person. That was when 911 was called.