A Holbrook man is accused of selling fentanyl that led to a woman's fatal overdose.

Jaquan Cassidy, 34, was arrested after he allegedly sold heroin and fentanyl to an undercover officer at the Holbrook Commons shopping center.

Authorities say they used the overdose victim's cellphone to lure him there.

Officials say the drug deal with the undercover officer happened on Aug. 25 - a week after a female from Lake Grove was found by her mother overdosing in the bathroom of their home.

The victim died a few days later at Stony Brook Hospital.

Police got hold of her phone and used it to message the suspected dealer.

Authorities say they set up a buy and arrested Cassidy -- an investigative technique that Suffolk County District Attorney Ray Tierney said is becoming more common with law enforcement.

"What our police have become adept at is getting the decedent's phone and going through whether it be phone calls, analysis of past phone calls or texts to try to make a determination of who gave this this poison that killed them," Tierney said.

"What's happening now are not overdoses, but poisonings," said drug treatment expert Steve Chassman, of the Long Island Council on Alcoholism and Drug Dependence.

Chassman said fentanyl is appearing in cocaine and phony prescription pills. He said the Long Island Council on Alcoholism and Drug Dependence offers free fentanyl test strips as well as the opioid antidote Narcan.

"The national drug supply is tainted and, unfortunately, it's leading to both fatal and non-fatal overdoses at a rate we've never before seen," Chassman added.

Nassau County police recently warned users about that uptick in overdoses and, so far this year, they have already made three fentanyl arrests.

In Suffolk, Tierney said they are combing through the suspect's contacts to find the source of the deadly drugs.

"He has indications that he dealt drugs extensively in the past," Tierney said.

Cassidy remains behind bars on $500,000 cash bail after he faced a judge on Friday.

The top charge Cassidy faces is criminal sale of a controlled substance.

If convicted, he could spend up to 12 years behind bars.

His next court date is March 3.