WASHINGTON HEIGHTS, Manhattan (WABC) -- Heroin-laced fentanyl was cooked up, weighed and packaged right across the street from a middle school in Washington Heights.Cops made the major bust as the drugs were being loaded into a livery cab.From the outside it looked like any other building in Washington Heights, but police say on the inside there was nothing ordinary going on.DEA agents and cops say they found up to three kilograms of heroin-laced fentanyl in one of the upstairs apartments."I was stunned. I've never seen that. I've been living here for quite a while," said Kenia Corporan, a resident.As if learning there was a heroin mill right on their block isn't shocking enough, residents say even more alarming is that directly across the street sits P.S. 115."It's sad. It's a sad thing because you got young people growing up and there's not a lot of opportunity for them and this is taking away their opportunity to learn," said Spike Chambers, a resident.DEA agents and cops raided the apartment on West 177th Street Thursday night and seized 5,000 prepackaged glassines of heroin.There were also dozens of stamps used for branding the drugs with names like "Godzilla," "Stink Face," "Spiderman," and "X-men" just to make a few.It makes residents wonder with names like that, were they targeting school kids?"It's frightening. The kids are right there. I went to that school. And it's to think that the kids, oh no," said Kenia Corporan, a resident.Three men were arrested for running the operation: Andres Cordero, Jose Luis Lugo and Anaury Burgos.