Firearms traffickers frequently operate across state lines, moving nearly 60,000 guns between states each year. Traffickers purchase guns — legally or illegally — in one state, and sell the weapons to criminals in other states to evade lifesaving gun laws.

Compounding this issue is the increased rise of untraceable, homemade “ghost guns.” Because they are sold in “do it yourself” kits, ghost guns are not considered “firearms” under the federal definition. These weapons are not subject to the laws that apply to gun sales — like mandatory background checks — or serial number requirements that allow law enforcement to trace guns used in crimes back to buyers.

It’s this loophole that makes ghost guns the weapon of choice for criminals.

In New Jersey, the number of non-serialized guns recovered by law enforcement has been increasing steadily: In all of 2019, law enforcement seized 55; so far in 2021, it’s seized 135, accounting for 5% of all gun recoveries statewide. In Pennsylvania, the rise is steeper. In Philadelphia alone, law enforcement recovered 99 ghost guns in 2019, 250 in 2020, and 382 already in 2021.

» READ MORE: Pa. Attorney General Josh Shapiro moves to reduce access to ‘ghost guns’

To stop interstate trafficking, our offices announced a partnership in 2020 — the PA/NJ Gun Trafficking Initiative. This effort is built on intelligence-sharing between law enforcement in Camden and Philadelphia and is making an impact to stop the violence fueled by guns.

Our regional partnership has already seen significant success in just a short time. Earlier this month, we stood together in Camden to announce the arrests of three men who operated a gun trafficking ring on both sides of the Delaware River. Our operation secured close to two dozen ghost guns, assembled in “build houses” in Philadelphia, transported across the river, and ultimately sold illegally on the streets of Camden. These unserialized, untraceable weapons included 10 AR-15-style assault rifles, high-capacity handguns, and a fully automatic handgun.

Last year, we announced the results of “Operation Zombie,” which led to the seizure of 38 firearms, including the weapon that killed 2-year-old Nikolette Rivera.

Collaboration breeds results. It is how law enforcement should work — here and across the county. It isn’t enough to stay in silos and fix the problems in only your communities, neighborhoods, or even states.

» READ MORE: A Camden gun trafficking ring is busted as state and federal officials target illegal weapons

And our work is not done. We must broaden the coalition of law enforcement keeping open lines of communication. We have met with our neighbors in New York, Delaware, Maryland, and Connecticut about creating a formal mechanism to share information on illegal gun trafficking and are pushing to have something in place soon.

But the onus can’t fall strictly on the states. We need to be able to see federal data. As it stands, local law enforcement is unable to access important gun trafficking and trace data from other states. New Jersey and Pennsylvania have pushed for greater data sharing at the federal level — most recently meeting with the Biden administration to demand greater access to gun-trafficking data. We have also worked closely with the ATF to shut the ghost gun loophole at the federal level.

Every neighborhood in Pennsylvania, in New Jersey, and across the country deserves to be safe from gun violence. Community members, law enforcement, state and federal partners: We are all in this together because we know that it’s going to take a multifaceted, unified approach to stop this violence.

The stakes are high. We live in a time when anyone seeking to do harm can go online and purchase an untraceable gun without a background check. Criminal activity is not bound by state lines — neither should our response.

Josh Shapiro is the attorney general of Pennsylvania. Andrew Bruck is the acting attorney general of New Jersey.