Two men received convictions Tuesday for their roles as ringleaders of a heroin distribution conspiracy.

Kewayne Hersel Carter, 39, and Raphael Cortez Ferguson, 37, were convicted of conspiracy to possess with intent to sell heroin in a drug-free zone.

Carter and Ferguson must serve eight years in prison without the possibility of parole, according to a news release from the Knox County District Attorney General. Carter’s sentence will run consecutively to a 15-year sentence in Michigan.

The release states Carter and Ferguson sold large amounts of heroin between October 2014 and April 2015. The two also sold a combination of cocaine and fentanyl that was sold as heroin during the same period.

“We continue to see individuals trafficking and purchasing what they believe to be heroin, but what actually contains some combination of fentanyl or its analogues,” said District Attorney Charme Allen in the release. “This creates a very dangerous situation for an addict who cannot tell the potency of the substance they are ingesting until it is too late.”

Carter, Ferguson and other co-conspirators would bring in large amounts of heroin from Detroit to Knoxville. The group would resell softball-sized amounts of heroin by folding them into cut portions of lottery playslips.

The substance the group trafficked changed from heroin to a combination of cocaine and fentanyl at some point, according to the District Attorney General’s release.

The release states fentanyl is up to 50 times stronger than heroin.