Two men living in South Jersey were crossing to Delaware to peddle heroin and fake Oxycodone pills that actually contained fentanyl, a more powerful and dangerous opioid, authorities say.

And the seizure of their stash is the largest in The First State’s history.

Julian Rivera-Villa, 56, and Ricardo Perez-Guillen, 40 were arrested last week, the U.S. Attorney’s Office in Delaware said in a news statement Thursday.

The two suspects are Mexican nationals who could serve up to 20 years in prison if convicted. They were living illegally in Gloucester City, authorities said.

Perez-Guillen was arrested last week after selling a kilogram of heroin and 600 fake Oxycodone pills in a Royal Farms convenience store parking lot in New Castle, Delaware. Rivera-Villa was arrested outside a mobile home he shared with Perez-Guillen.

There, investigators found about seven kilograms of heroin, three kilograms of cocaine, 14,000 pills and more than $28,000 in cash. Another two kilograms of heroin was found in two hidden compartments in a vehicle.

Authorities grew suspicious of the pills because they were selling for far less than true Oxycodone. “There has been a recent surge in the Tri-State area of fake Oxycodone that are in actuality laced with fentanyl," a DEA task force officer wrote in a federal complaint.

Rivera-Villa was handed over to the federal Immigration and Customs Enforcement (ICE) because he was previously deported from the U.S. for a criminal offense, court documents say.

-This article contains information from The Associated Press.

Joe Brandt can be reached at jbrandt@njadvancemedia.com. Follow him on Twitter @JBrandt_NJ. Find NJ.com on Facebook.

Have a tip? Tell us. nj.com/tips

Get the latest updates right in your inbox. Subscribe to NJ.com’s newsletters.