Four men were arrested and charged in New Jersey on Monday for allegedly conspiring to sell untraceable assault rifles assembled from online kits known as “ghost guns,” authorities said.

It’s the first time people have been charged under a new state law that makes it illegal to buy, build, or sell these often plastic, but deadly firearms. The “ghost guns” were ordered online without serial numbers and came with instructions on how to finish them to be functional firearms, authorities said. They were allegedly sold for $1,100 to $1,300 each—twice the price of a legal assault rifle.

“Assault rifles like these pose an especially deadly threat to law enforcement, innocent bystanders, and others when placed in the wrong hands, and suffice it to say no one conducted any background checks here," Attorney General Gurbir Grewal said in a Monday press conference. “They are not registered. They don’t have serial numbers and they are sold without any background check process whatsoever.

In what authorities call “a landmark investigation,” the four men were among a dozen arrested in connection with a cocaine trafficking operation, who allegedly thousands of dollars worth of drugs, New Jersey authorities said.

The year-long investigation, which authorities called “Operation Stone Wall,” originally focused on a cocaine distribution network in Lindenwold, New Jersey. During the operation, investigators intercepted a conversation discussing a delayed gun sale “because they could no longer have guns shipped to New Jersey, due to the new criminal law,” the attorney’s office said in a press release.

“We need to go across the border,” one of the suspects allegedly said in the call, according to Gurbir.

Prosecutors allege to get around the law, which was enacted in November, the men had gun parts shipped to Pennsylvania. Those parts were eventually intercepted by authorities in Bensalem, about half an hour outside of Philadelphia, last week.

On March 13, authorities intercepted parts for two “ghost guns” that were being shipped to Bensalem and arrested the four men involved.

Investigators also seized 525 grams of cocaine, three bundles or 30 doses of heroin, and 13 guns, including the six ghost gun AR-15 assault rifles in a series of raids that led to some arrests earlier in the month.

“The reason why we sought that law and the reason why the governor and the legislature stepped up to pass it and enact it is because “ghost guns” are a real and dangerous menace,” Grewal said. “They offer criminals, convicted felons, terrorists, domestic abusers — people who we all agree should not own firearms — the ability to access them.”