NOGALES — Customs officers stationed at the commercial border crossing in Nogales made the largest fentanyl seizure ever recorded at any port of entry in the United States the day after President Donald Trump signed a bill putting an end to the longest government shutdown in history.

According to U.S. Customs and Border Protection, a canine officer alerted other officers to the presence of 254 pounds of fentanyl inside a hidden floor compartment of an 18-wheeler carrying cucumbers, during a secondary inspection at the Mariposa port of entry just past noon on Saturday.

"It has been sent for a chemical analysis so we won't know the purity until a much later date," said Michael Humphries, the port director for Nogales.

He noted just how deadly that amount can be in very small doses. The synthetic opioid is 80 to 100 times more potent than morphine, according to the Drug Enforcement Administration.

Saturday's bust contained enough fentanyl to kill more than 115 million people, according to investigators in the case. That's the equivalent of a third of the entire U.S. population.

In addition to the fentanyl, officers also seized 395 pounds of methamphetamine hidden inside the compartment in the 18-wheeler.That was the third largest seizure of its kind along the Arizona border, CBP said. Combined the two drug busts have an estimated street value of $4.6 million.

The smuggling of both opiates has been on the rise through ports of entry in recent years along the U.S.-Mexico border, Customs and Border Protection statistics on drug seizures show.

But even so, the seizure on Saturday was both surprising and alarming, according to Guadalupe Ramirez, who oversees all border crossings in Arizona.

"Normally, the southwest border ports are intercepting the most fentanyl, compared to other ports of entry, airports, seaports, the northern border," he said, noting that Nogales is one of the key routes.

"This is the largest fentanyl seizure in any port of entry," he said. "In CBP, in the history of CBP, this is the largest fentanyl seizure."

The 254 pounds seized just on Saturday in Nogales is more than the 155 pounds of fentanyl that officers seized at all six border crossings in Arizona during the last fiscal year.

MORE: Most drugs get smuggled through ports of entry. A wall won't stop it.

Juan Mariscal, Homeland Security Investigations' assistant special agent in charge for Nogales, is tasked with investigating Saturday's smuggling attempt.

He said the driver, a 26-year old man from Mexico, is in federal custody, and faces two charges for possession with intent to distribute.

"No other arrests have been made so far. However, my agents are continuing with the investigation," he added.

Humphries said that given the potency of the drugs, officers working that day took additional precautions to handle and avoid exposure to the narcotics. That included having officers use protective gear, and handle it in an open-air setting to avoid trapping it inside the customs building, he added.

"We package it, we tape it up. If we cut an area, we secure it," he said. "We have some smaller amounts that will go inside a smaller bucket, that bucket will be taped and that bucket will be placed in a larger bucket. That bucket will be secured and taped so we have to make sure there will be no accidents."

Those buckets and containers were on display Thursday during a news conference from the Mariposa crossing. CBP said it will keep the drugs seized Saturday as evidence in the prosecution of this case. After that, the drugs will be incinerated.

As an additional precaution, officers also destroyed the shipment of cucumbers inside the 18-wheeler.

Nogales is at the peak of the winter produce season. Millions of pounds of winter produce cross the border each day from Mexico to supermarkets all along the western United States.

An average of 1,500 trucks cross each day through the Mariposa commercial crossing during this time, according to Customs and Border Protection in Arizona.

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