DETROIT (AP) – Two men were arrested in what law enforcement officials are calling a breakthrough in their investigation into a lethal form of heroin blamed for more than 100 deaths in the Detroit area.

Wayne County sheriff’s deputies and federal drug agents said the two suspects arrested Thursday sold a mix of heroin and the prescription drug fentanyl from the Jeffries housing project north of downtown.

Sheriff Warren Evans said investigators believe one of those arrested, a 45-year-old Detroit man, was “the key player who supplied the Jeffries project,” while the other was a lower-level dealer caught selling drugs to an undercover deputy.

“We have made a dent in what has been a crisis in this community,” Evans said.

Fentanyl, a legally produced painkiller, is 80 times stronger than morphine. Officials in cities from Chicago to Philadelphia have reported a total of more than 200 deaths from the combination. In the Detroit area, the fentanyl-laced heroin has been sold on the street as “Magic” or “A-1,” officials said.

The two men, who were being held at the Wayne County Jail, had not been formally charged when the arrests were announced Friday morning and their names were not immediately released.

Officials say the man Evans described as a distributor was carrying more than 80 individual packets of the heroin mix at the time of his arrest. The man’s home also was searched and officials found heroin, marijuana, suspected packets of pure fentanyl, three handguns, a shotgun and about $5,000, authorities said.

In Chicago, federal prosecutors on Wednesday charged more than three dozen gang members with running a drug ring that sold both heroin and individually packaged fentanyl. Officials said none of the heroin seized in that bust was found to be mixed with the painkiller.