A former Wesleyan University student pled guilty in a New Haven federal court Thursday to charges of distributing synthetic drugs.

The student, Zachary Kramer, pled guilty to charges of distribution and conspiracy to possess with the intent to distribute MDMA, commonly known as Molly. Kramer’s charges stem from a monthslong investigation into the distribution of controlled substances that caused multiple Wesleyan students to overdose in February of this year, according to a press release from U.S. Attorney’s Office spokesman Tom Carson. Kramer began purchasing and reselling Molly to students at Wesleyan in September 2014. He was arrested on federal charges May 22 and released on bond the same day, the press release stated. The maximum term of imprisonment that Kramer faces is 20 years as well as a maximum fine of $1 million, but his sentence is subject to change pending sentencing next February.

“The defendant acknowledges that he is entering into this agreement and is pleading guilty freely and voluntarily because he is guilty,” Kramer’s plea reads.

Deirdre Daly, U.S. attorney for the district of Connecticut, and Robert Spector, assistant U.S. attorney for the district of Connecticut, submitted Kramer’s indictment on May 21. According to the indictment, 11 individuals — 10 of whom were Wesleyan students — overdosed on Feb. 21 on what they believed was Molly, but was actually AB Fubinaca, a Schedule I controlled substance. According to the Drug Enforcement Administration, Schedule I controlled substances are considered the most dangerous class of drugs because of their high potential for abuse and the potential for severe dependence.

According to the indictment, two of the students who overdosed were judged to be in critical condition, and one of the students had to be revived after his heart stopped. All of the students obtained the drug through distributors whom Kramer directly supplied, the indictment said.

Kramer supplied controlled substances to a number of other distributors. Though he and many of the distributors destroyed the drugs they had in their possession, the Middletown Police Department managed to seize a sample of the substance from one of the distributors in February. The toxicology report indicates that the substance did not contain MDMA. But Kramer will be held accountable for the amount of substance he supposed to be MDMA that he intended to distribute, the indictment said.

Arrest warrants were issued for three other students alongside Kramer. Only two of these students, including Kramer, face federal charges.

Before Kramer became the primary supplier of Molly at Wesleyan, he distributed illegal substances to students after buying them from Eric Lonergan, another former Wesleyan student who was indicted for similar crimes. Lonergan began buying and selling the drugs in November 2013, according to his indictment.

Before the February 2015 incident, Lonergan sold a substance to a group of students in September of last year, several of whom subsequently had adverse reactions within 15 minutes of ingestion. Afterwards he sent some buyers a video of him testing the substance to prove that it was MDMA. But a toxicology report on a sample of that batch of drugs sent in by one of the buyers indicated that the substance did not contain MDMA. The test showed that the substance was a combination of AB Fubinaca and 6-MAPB, an uncontrolled substance analogous to MDMA.

Lonergan’s plea hearing is scheduled for Nov. 23 before Judge Joan Margolis.