WEST PIKELAND TOWNSHIP, Pa. (CBS) — In an exclusive CBS3 investigation, Commissioner Richard Ross says 21 year veteran of the force narcotics officer Stanley Davis is facing imminent federal charges.

“He got into some illicit behavior while assigned to the FBI, they uncovered it, and made us aware,” Ross said, confirming the existence of the ongoing federal probe.

The story of the officer’s downfall has some twists. It began along the Pennsylvania Turnpike in Chester County.

It was Nov. 16, the location of a single vehicle crash in the westbound lanes in West Pikeland Township, a couple miles from the Downingtown interchange.

On the roadside was the driver – an injured Rosie Forsyth from York County.

A state police corporal wrote in arrest papers: “It is my opinion that at the time of the crash, she was under the influence of a drug…”

Forsyth’s grandmother, Thelma Frey, 90, one of two passengers in the car, was critically hurt. Both went to the hospital. Forsyth claimed she lost control of her Volvo S-60 as she tried to give her grandmother a drink.

As for drug use, she allegedly told troopers she had not used heroin in five or six days and says she last took 30 milligrams of methadone 12 hours before the crash.

But in arrest papers, troopers said they found: “numerous puncture sites about both arms.”

Forsyth was charged with a host of moving and drug violations. Eight days later, her grandmother died from her injuries. Charges were ramped up. Forsyth was slapped with a felony count of accidents involving death.

That’s where the crash investigation concludes, but it’s not the end of the story.

The source of that heroin, that investigators say caused the deadly crash, is now the focus of a federal investigation.

Multiple sources confirm officer Davis, who abruptly retired last week, provided heroin confiscated from busts to Rosie Forsyth.

Sources close to the case say heroin supplied by the police officer can be directly tied to the crash that killed the grandmother.

Commissioner Ross wouldn’t elaborate on specifics about the ongoing FBI investigation but said: “I anticipate probably within the next week or so, he will be charged. He is no longer a police officer. I will tell you it was completely illegal, and so there was nothing mistake-laden in the sense of a mistake of the heart or mind – this was illegal, what he did.”

Numerous attempts to reach Stanley Davis and Rosie Forsyth were unsuccessful. CBS3 spoke to Forsyth’s public defender who declined to comment.