KENOSHA, Wis. (AP) — A preliminary hearing for two Wisconsin brothers accused of running an illegal operation to manufacture vaping cartridges with THC oil has shed new light on how authorities cracked the case.

Detectives testified during Thursday’s hearing in Kenosha that they busted a man selling the illegal cartridges in Waukesha. He then became a confidential informant and led them to 20-year-old Tyler Huffhines, the alleged masterminded.

His 23-year-old brother, Jacob Huffhines, is also charged in the case. Their arrests this month came as authorities investigate hundreds of cases of a severe lung disease linked to vaping. No illnesses have been tied to the operation.

A judge ruled there was probable cause to bind the Huffhines brothers over for trial.

The brothers are expected to enter pleas at their next hearing Oct. 23.