Nearly 500 pills believed to be laced with fentanyl were found in the Grand Forks, N.D., region last week as part of an investigation involving the deadly opioid drug.

Officials also arrested six people, ranging in age from 19 to 22, from the area who had possession of the pills.

The blue pills were marked with "A 215," an imprint usually found on oxycodone pills. They may have been responsible for up to three overdoses in the area in the past week, according to Grand Forks police.

A probable cause statement filed by the Polk County Attorney's Office detailed the investigation:

On March 22, officials found an unconscious man who later said he had snorted a blue pill with the "A 215" imprint. The man told police he had heard people were selling fake oxycodone pills that actually contained fentanyl.

The following week, East Grand Forks police arrested two people found with multiple drug paraphernalia, including a handful of the blue pills. One of the people arrested was a 20-year-old woman who said she was pregnant.

Investigators were led to 19-year-old Tucker Christian Collings of Grand Forks and found 160 blue pills in his home. In front of officials, Collings messaged a friend he said sold him the pills, telling him they "went like hot cakes."

Two hundred more pills were found during a search of the friend's home. East Grand Forks police interviewed another man who said he had received pills from Collings and was selling them for $20 to $40 a pill.

Drug agents searched the vehicle of another man possibly connected to the distribution and found 100 blue pills.

Arrested last week were were Cody Allen Stengl, 19; Robert John Benson Powell, 20; Benjamin David Gottberg, 19; Joel Anthony Ryan, 22, all of East Grand Forks, and Leah Anne Sourdif, 20, of Grand Forks. All appeared in Polk County District Court on Thursday and have further hearings April 4.

Collings was arrested and faces criminal charges in North Dakota.

Grand Forks police believe up to 300 of the pills are still unaccounted for. Police, along with the Grand Forks Narcotics and Pine to Prairie task forces, continue to investigate the distribution.

According to the Polk County Attorney's Office, "numerous individuals" have overdosed and died in the Red River Valley by ingesting fentanyl and combining it with drugs such as heroin.

Officials in early March reported an alarming rise in the amount of drugs seized last year, particularly methamphetamines and opioids. They noted that fentanyl is arriving in Minnesota from China.