A self-described drug addict stood by a vacant lot on the city's South Side and pointed down the block. There, he says, more than a dozen of his friends and acquaintances died after using heroin laced with a strong painkiller.

"Joe died down there, and then there was Rita, Cherlyn, Marvin died somewhere over there — and Chico there," said Don Howard, 59, flanked by rows of derelict buildings and a sign atop a lamppost that read, "Chicago Blues District."

Several miles away, police and drug enforcement officials ended two days of discussions on the possible source of the bad heroin that killed Howard's friends and at least 100 others from Chicago to Philadelphia.

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"In my almost 30 years of law enforcement experience, I haven't seen a threat that concerns me this much," said Tim Ogden, an agent with the U.S. Drug Enforcement Administration's Chicago office. "Fentanyl is a very, very potent substance."

The summit that ended Thursday provided officials from 12 states and Washington, D.C., the chance to coordinate their investigations into the spike of fentanyl-related deaths since the beginning of this year, Ogden said at a news conference.

Fentanyl is a legally produced prescription painkiller that is 80 times stronger than morphine. But the type of fentanyl currently being mixed with heroin is most likely manufactured in illicit labs, Ogden said.

He said that just 125 micrograms of the illegal fentanyl — the equivalent of a few grains of salt — are more than enough to kill.

"I view fentanyl use as taking a six (chamber) revolver, putting five bullets in it, putting it to your temple and pulling the trigger," he said.

There were outbreaks of fentanyl-laced heroin in the '80s and early '90s, said Arlington, Va.-based DEA spokeswoman Mary Irene Cooper, who was in Chicago for the meeting. The difference is that the outbreaks aren't isolated this time to one city.

"We're trying to figure out why it's spreading so widely," she said.

Its deadliness doesn't appear to have dissuaded hardened drug addicts.

After Chicago police publicized one street corner where samples of fentanyl-laced heroin had been handed out — thinking addicts would steer clear of the area — drug users flocked there hoping to score free heroin, Police Supt. Philip Cline said.

"We have willing victims here," he said. "That's part of the problem."

In Chicago, there have been more than 60 confirmed fentanyl overdoses since April, 2005, with the vast majority of them coming this year, the DEA said. Deaths caused by fentanyl-laced drugs have also been reported in Michigan, Missouri, Ohio, Pennsylvania, New Jersey, Delaware and Maryland.

Howard said there is less fear among many addicts than non-addicts might presume.

"Some addicts are frightened, but others aren't," he said. "They just feel that if it's their time, it's their time."

"Suicidal behavior comes from being an addict," agreed Francois Seets, a 58-year-old recovering addict from Chicago. "They think they're immortal. ... And they think it (the fentanyl contamination) will pass."

So infinitesimal are the amounts of fentanyl, Seets said, that there is virtually no way of determining whether a bag of heroin is laced with it. The fentanyl wouldn't affect the taste or look of the narcotic, he said.

"You wouldn't know it's bad until you collapse," he said.

Howard, who said he struggles to scrape together the $10 it costs for a small bag of heroin, said he doesn't turn down free samples of heroin — even though such samples have been linked to the recent fentanyl deaths.

But he does take precautions.

Before settling down to shoot up a sample with friends, "I let somebody else go first to be sure," Howard said.

Seets said the fentanyl outbreak does serve as an inspiration to him, driving home the potentially deadly consequences of a relapse.

"It makes me understand I am mortal," he said.