Homeless and the danger is obvious. People are falling over [ indiscernible ] we had to call 911 for four people because they were having problems from it from k2. Reporter the substance can trigger a violent reaction. The nypd released this video that shows a naked homeless man under the influence in the street blocking a School Safety vehicle in brooklyn. Witnesses to the unpredictable behavior describe it as frightening. Every time i get off this train, i got to worry about being harassed by people that use this k2. Reporter how do you know they are using it . Acting. You can see they are violent in nature. Reporter another issue the homeless can buy it for as little as a dollar from bodegas illegally selling it. Just last week investigators seized 10,000 packets. These individuals many of them under the influence of this drug totally crazy that, um, super human strength, impervious to pain. Reporter today we asked police why they doesnt stop this use out in the open since we spotte