An Alabama veterinarian was arrested this week after local and federal law enforcement discovered he used Bitcoin to purchase nearly 36,000 doses of fentanyl on the dark web, AL.com reported .

Dave Ray Wallace—a 46-year-old from Alabaster and a practicing veterinarian in the nearby town of Trussville—and Dana Marie Leslie of Pelham were taken into custody Monday in Shelby County for trafficking the narcotics.

While the arrests happened in Alabama, the investigation first started in New York. Law enforcement officers in the state caught wind of a package of fentanyl set to be delivered to a resident in Shelby County.

The package was intercepted at John F. Kennedy International Airport and contained a teddy bear that was stuffed full of fentanyl in order to conceal it.

The officers in New York informed law enforcement in Alabama of the intended recipient of the package, which Shelby County investigators used to identify addresses associated with the individuals who ordered the fentanyl. During that investigation, it was discovered that one of the parties, Wallace, was a practicing veterinarian.

In total, Wallace is believed to have purchased more than 36,000 doses of fentanyl. Most of the purchases were made on the dark web—a collection of sites that can only be accessed by special web browsers. The dark web is often associated with sales and trades of illegal goods including firearms and drugs.

Wallace made most of his purchases using the popular cryptocurrency Bitcoin. Because it is a digital currency and provides more anonymity than standard payment methods, Bitcoin transactions can be difficult to track and associate with an individual, making it a popular option for the purchase of illicit goods.

In total, about 18 grams of fentanyl were seized from Wallace and Leslie during the arrest. Less than a 2mg dosage of fentanyl can produce fatal results for users.

Both Wallace and Leslie were arrested Monday and charged with conspiracy to commit a controlled substance crime. As of Tuesday, they both remain held without bond in the Shelby County Jail.

Fentanyl, the drug the two were allegedly purchasing, is a synthetic opioid used for pain management. According to the National Institute on Drug Abuse, fentanyl is similar to morphine but 50 to 100 times more potent. Fentanyl is often mixed with or substituted for heroin.

Like other opioids, fentanyl binds the body’s opioid receptors, which are found in the parts of the brain that control pain and emotions. As a result, dopamine levels in the brain are increased and can produce a state of euphoria for the user.

According to a recent report from the U.S. Centers for Disease Control and Prevention, fentanyl has also become one of the most deadly drugs in the country. More than half of recent opioid overdose deaths in 10 states were related to the powerful painkiller.