Traces of methanol were found in the bodies of 21 teenagers who died after celebrating at a South African nightclub in June. Government officials joined police at a press conference on Tuesday to reveal the latest details in the case, The Washington Post reports. While the substance was detected in the blood samples of the teens, experts said they’re still assessing the methanol levels to determine whether the amounts were “lethal” or “nonlethal.”

The teens, who were between the ages of 13 and 17, died after being at the Enyobeni Tavern in the coastal city of East London on June 26. Police said some of the victims were slumped over tables and chairs when officers arrived.

Health officials initially suspected that alcohol and carbon monoxide poisoning could have been possible causes of death. Litha Matiwane, the Eastern Cape provincial deputy director for clinical service, said initial tests ruled out those factors. Some reports also indicated that a stampede may have been to blame.

Yonela Dekeda, a spokeswoman for the Eastern Cape Health Department, told the Post that “there are more tests that are being done to identify exactly what the cause of death was.”

“We can’t say at this stage where they got the methanol, whether it was through liquor or something else. That is still unknown,” Dekeda continued.

Methanol, which can cause various health issues, is often found in fuels, plastics, pesticides, paint and antifreeze, according to the CDC.

“Most methanol poisonings occur as a result of drinking beverages contaminated with methanol or from drinking methanol-containing products,” the CDC states.  “In the industrial setting, inhalation of high concentrations of methanol vapor and absorption of methanol through the skin are as effective as the oral route in producing toxic effects.”

One witness who spoke with the Post said people were heard in the tavern, yelling  “I can’t breathe” and “I’m choking.” Others said people were being “suffocated” by a substance that “smelled like gas.”

The 52-year-old owner of the Enyobeni Tavern, who was arrested in June, is expected to appear in court next month. The owner faces multiple charges, including supplying underage people with alcohol. Two employees, ages 33 and 34, have also been arrested.

As Blavity previously reported, the students were celebrating the end of their high school exams when the tragedy unfolded.

“They died as they danced,” Police Minister Bheki Cele told CBS News. “They dance, fall and die. Literally.”