Federal health officials say they’ve identified the likely culprit behind a vaping-related lung illness that’s sickened thousands and killed dozens. Investigators found Vitamin E acetate in the lung fluids of 29 people who reported getting sick from vaping, the Centers for Disease Control said Friday. The oil was found at the “primary site of injury” of these patients, CDC principal deputy director Anne Schuchat told reporters in a Friday news conference.

So far, at least 39 have died and over 2,000 have become sick according to the CDC’s most recent figures. While Vitamin E acetate has long been suspected as the likely culprit, Friday’s announcement is the first time the CDC has acknowledged publicly that it was such. The rash of deaths related to electronic cigarette use has led several municipalities and states to enact various forms of vaping bans, from moratoriums on the sale of flavored vapes to San Francisco’s ban on all e-cigarettes. The Trump administration has moved to ban flavored vaping products nationwide, with a rollout expected in the coming months.

Schuchat said CDC labs tested for a wide variety of compounds, including other oils and distillates. While she would not rule out the possibility of other oils making people sick, she described the lab results as a “breakthrough” in the investigation, as no other toxins were detected in those sick.

The results from the 29 patients where Vitamin E acetate was found include both those that have gotten sick and recovered, and those that had died. In 23 of these, THC was also found.

Vitamin E acetate is found in both foods and cosmetic products, especially topical creams. Ingested or placed on the skin, the oil is harmless. However, inhaled it damages the lungs, causing symptoms of cough, shortness of breath and chest pain — and in high concentrations, coma and death.

Investigations over the past few months found that illicit cannabis cartridge makers were using the oil as a cutting agent or additive to fill up cartridges on the black market. At least one of the victims who fell ill reported purchasing a cartridge at a legal cannabis dispensary. In some cases, the oils were found to make up the majority of the oil in those cartridges.

This is a breaking news story and will be updated with the latest developments.