Authorities are also still tracing a vast and shadowy distribution network in which empty cartridges are filled with THC-laced liquid in “pen factories,” packaged with boxes available online and often shipped across state lines in trucks or rental cars.

“It is something we’re trying to get our hands around,” said L.J. Fusaro , the chief of police in Groton, Conn., where officers confiscated 435 THC cartridges in a bust this year. “As of late, it’s really become of interest to law enforcement because of the harm that’s come to folks, particularly our youth.”

In August, Illinois health officials announced the first vaping-related death in the nation. In the weeks after, more deaths in Kansas, California and Indiana were tied to the ailment, and that number has continued to grow. Illicit THC-filled vaping cartridges with labels like “Dank Vapes” could be culprits, according to health officials, but it is still unknown what is making people ill.

In police circles, efforts have turned to trying to get a handle on the universe of vaping products — a wide, disparate array of sources of cartridges and a murky and fragmented distribution network for them.

Law enforcement officials have found a flourishing black market of vaping cartridges that are made in small operations, often in a house or apartment. The cartridges are filled with THC oil and often diluted with substances that are dangerous to inhale, like vitamin E acetate, one of the products that health officials suspect has caused lung damage. Then they are sold on the street or online for roughly $20 each.

In recent years, the police have sometimes struggled to classify vaping materials in official reports and to decide which criminal charges should apply to them.

“We started recognizing it as commanders from across the state were calling us, trying to figure out how to report them to us, because they didn’t fit into a category,” said Brian Marquart, the statewide gang and drug coordinator at the Minnesota Department of Public Safety .