The tip came to Minnesota police officers in July via a confidential informant: In a suburb in Anoka County, the informant said, a man had been quietly selling thousands of vaping cartridges laced with marijuana from his home.When authorities entered the man's condominium last week, they found a staggeringly large stash of vaping cartridges, believed to be one of the biggest busts in the country. Close to 29,000 cartridges were tucked away inside a Cadillac Escalade. Another 30,000 were stacked in a garage. Some were packaged in black boxes with colorful lettering, cheerful images of Fred Flintstone and names of candylike flavors like mai tai, strawberry shortcake and Fruity Pebbles.They were the sorts of vaping products that have been identified as possible culprits in a perplexing lung illness that has sickened at least 800 people across the country and killed at least 16.As health officials grapple with a public health crisis they are struggling to understand, police departments are in the midst of a swift crackdown on vaping products containing THC, the psychoactive ingredient in marijuana. In the Phoenix area, authorities recently raided three homes over eight days, seizing hundreds of THC cartridges at each. In Wisconsin, detectives arrested two young brothers accused of running a large-scale THC cartridge assembly operation inside a condo. And in Nebraska, sheriff's deputies found a stash of cartridges in a car parked at a truck stop.Until recently, some police departments busy fighting a national opioid epidemic had considered illegal vaping products a nuisance, but not a lethal threat. Police departments had taken small steps to root out illegal cartridges, but as more teenagers and young adults have begun vaping THC, sometimes with deadly consequences, authorities say they are now paying close attention."It's become an absolute priority," said Sheriff Paul Penzone of Maricopa County, Arizona, where deputies have made undercover purchases from vaping cartridge dealers and tried to disrupt a sprawling supply chain.The effort to crack down on illicit vaping products has been laden with complications. Police say they have been stunned by the growth in popularity and variety of vaping devices. Enforcement can be difficult because vaping THC is not accompanied by the distinctive -- and often incriminating -- smell of marijuana. And police officers have had to learn the difference between vaping cartridges for THC, which are illegal for recreational use in most states, and devices for vaping nicotine, which are legally sold at many drugstores and gas stations.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, Connecticut, 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, 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.Authorities have tracked down illegal vaping operations through elaborate police investigation -- but also fortuitous traffic stops.In Indiana, 50,000 cartridges worth $1 million were found on a box truck traveling from California to Indianapolis after the driver was pulled over in March for following another vehicle too closely. In Nebraska, the State Patrol has netted three seizures of illegal vaping products in recent weeks, including the discovery of thousands of THC cartridges in the bed of a white pickup truck that made an improper lane change west of Lincoln.Some boxes of cartridges have been found in plain sight -- a reflection, perhaps, of the relative newness of efforts to crack down on THC cartridges and of states' differing laws on marijuana."It's not like it's unmarked and heat-sealed and hidden in a false compartment," Capt. Jason Scott of the Nebraska State Patrol said. "It's usually just right out in the open."Other cases have involved lengthy and intense investigations. In the Minnesota case, an undercover officer from a drug task force bought vaping products from Valentin V. Andonii, 22, then followed him to his home, leading to the discovery of nearly 77,000 cartridges.Alyssa Jones, a lawyer for Andonii, declined to comment on two felony drug charges her client faces, each of which could carry a 30-year prison term if he is convicted.Federal officials have also targeted illegal vaping, though local and state law enforcement agencies said they have mostly been operating on their own. In Ohio, three people were indicted in May after Drug Enforcement Administration agents found thousands of THC vaping cartridges. And last year in North Carolina, federal agents arrested a man accused of selling a synthetic marijuana vaping product.The threat of THC-laced vaping cartridges still pales in comparison to the pervasive presence of opioids, which killed more than 47,000 people in overdoses in 2017. Some police departments may have been so busy battling heroin, fentanyl and other drugs that they did not view THC vaping as a threat until very recently."Honestly, I think we kind of missed the boat a little bit because we've been dealing with opioids," said Fusaro of the Groton, Connecticut, police. "In some respects, we didn't see this coming."In places like Phoenix, where Penzone's deputies recently confiscated 1,100 cartridges, there is a growing sense of just how pervasive illegal vaping has become and just how hard it will be to choke off the supply."Through e-cartridges, we now have a pathway where our children can ingest literally any drug," Penzone said. "That creates a whole new challenge for us that we've never seen in the past."This article originally appeared in The New York Times.(C) 2019 The New York Times Company