PROVIDENCE, R.I. — A Providence man has agreed to plead guilty to selling a deadly synthetic drug and threatening a witness, according to an agreement filed in U.S. District Court in Providence.

Victor Burgos, 20, agreed in papers filed Aug. 20 to plead guilty to charges he possessed and distributed acetyl fentanyl, a new kind of injected illegal opiate that resembles heroin, though it is much more potent. It has killed 14 people in Rhode Island this year and dozens more elsewhere, according to health officials.

Burgos also agreed to change his plea to guilty on a charge of tampering with a witness.

He is scheduled to change his plea during a hearing Sept. 6 before U.S. District Judge William Smith.

Burgos, who is known as “Fatboy,” was arrested May 17, within days of when authorities have said he sold acetyl fentanyl to a confidential informant. Police thought the informant was buying heroin, but tests later showed that it was acetyl fentanyl. Burgos was charged with possessing and distribution of synthetic acetyl fentanyl and ordered released with an electronic monitoring system May 21.

On June 3, police said Burgos went to the informant’s home and spoke with his mother, saying he knew it was her son who had ratted on him, and telling her the son was “going down.”

“I have nothing to lose and I am going to spend the rest of my life in jail because of all those overdose deaths,” Burgos allegedly told the woman.

Police said he also pulled down his sock, revealing what the mother believed to be a gun.

The Rhode Island Department of Health has said 14 people died in the state between March and May after using acetyl fentanyl. The deaths prompted a health advisory by the U.S. Centers for Disease Control warning health officials nationwide about the potent new drug.

Pennsylvania health officials have said at least 50 deaths there were due to the drug, and have warned drug users in the state that acetyl fentanyl can resemble heroin and has the same consistency and color.