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A Stillwater prison inmate's fatal overdose has officials investigating how the illicit drugs made their way into the facility.

Castle R. Ahlbeck, 30, was found by prison staff unresponsive in his cell late Monday morning, said Minnesota Department of Corrections (DOC) spokesman Nicholas Kimball.

"Upon discovery, DOC staff attempted life-saving measures and outside emergency medical services were requested and responded to the facility," a statement from Kimball read.

Ahlbeck was pronounced dead at the scene, Kimball said.

There have been five deaths from drug overdoses in DOC facilities since 2015, according to the agency.

Prison staff saw in Ahlbeck's cell "substances and paraphernalia that appeared consistent with possible narcotic use," the statement continued. Preliminary testing revealed the substances to be methamphetamine and fentanyl.

Official cause and manner of death will be determined by the Ramsey County Medical Examiner's Office.

In the meantime, DOC investigators and local law enforcement are "actively investigating how the drugs were introduced to the facility, and investigators are working several leads related to the source of the controlled substances," Kimball's statement read.

Kimball added in an e-mail that observational rounds by prison personnel "occur regularly around the clock in the units to confirm people are where they're supposed to be, and ... those rounds happened Sunday night/Monday morning."

Ahlbeck, of Brooklyn Park, was serving a sentence of more than 13 years for shooting another man in the leg outside an East Bethel convenience store in 2016 after a drug deal. After the shooting, he fled police at speeds of 120 miles per hour before crashing and being shot by law enforcement.