Authorities continue to investigate a wave of overdoses linked to a superstrong batch of heroin circulating in Butler County.

The investigation is a priority and some progress has been made, according to county District Attorney Richard Goldinger.

“We have some leads about who may be the source of this,” Goldinger said this morning. He did not cite specific information.

Investigators have spoken to some of those who overdosed last week in hopes of tracking down the source of the drug, according to county Detective Tim Fennell, who leads the county Drug Task Force,

If identified, the seller of the heroin could face a top charge of drug delivery resulting in death, a first-degree felony that can result in a multiple-year sentence for dealers.

The “extremely strong batch of heroin” is believed responsible for at least two deaths and as many as a dozen near fatal overdoses in the past week alone, said Fennell,

He and Goldinger on Friday took the unusual step of issuing a public warning about the potentially lethal heroin.

The advisory was prompted after authorities learned of at least five near fatal overdoses handled Friday during one shift at the Butler Ambulance Service.

Investigators suspect toxic batch of heroin comes in light blue stamp bags with no markings or names on them.

Fennell said he believes the potentially deadly heroin is “localized” and apparently has not hit other counties, such as the lethal batch of so-called “Theraflu” did last year.

In 2014, at least 22 people in Western Pennsylvania, including three in Butler County, died from a single batch of fentanyl-tainted heroin stamped with the name Theraflu.