The alleged leader of a drug trafficking organization based in San Diego and Tijuana appeared in court on Tuesday to face federal charges in relation to multiple drug seizures, including a 2021 bust of 2 kilograms of powdered fentanyl that is the most concentrated ever tested by the Drug Enforcement Administration’s (DEA) southwest laboratory, the U.S. Attorney's Office announced.

Aaron Leib Kobisher, 34, allegedly headed a drug trafficking organization that smuggled fentanyl, methamphetamine and cocaine from Mexico to San Diego for distribution in the U.S., prosecutors said.

Kobisher, who also goes by the name "El Kobi," was extradited from Spain to face charges, having been arrested there in June. He had previously fled the U.S. to Mexico in November 2022.

A Drug Enforcement Administration (DEA) chemist checks confiscated powder containing fentanyl at the DEA Northeast Regional Laboratory in 2019 in New York. A 2021 bust of 2 kilograms of powdered fentanyl is the most concentrated ever tested by the DEA's southwest laboratory. (Don Emmert/AFP via Getty Images)

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Kobisher made his first appearance in federal court on Tuesday following his extradition and faces fentanyl, methamphetamine, and cocaine trafficking charges. 

He is the lead defendant charged in a six-defendant indictment stemming from a long-term investigation, prosecutors said. Four others charged in the same indictment were arrested earlier this year while one defendant remains a fugitive.

If convicted, Kobisher faces up to life in prison and a $10 million fine. 

U.S. Attorney Tara McGrath said that fentanyl is a very dangerous drug and these seizures are hugely significant.

"Fentanyl is deadly in all forms, but one of the seizures in this case packed an extraordinary punch," McGrath said.

DEA drug testing

A Drug Enforcement Administration (DEA) chemist checks confiscated powder containing fentanyl at the DEA Northeast Regional Laboratory in 2019 in New York. A 2021 bust of 2 kilograms of powdered fentanyl is the most concentrated ever tested by the DEA’s southwest laboratory. (Don Emmert/AFP via Getty Images)

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"Getting fentanyl out of the hands of drug traffickers – especially the most potent versions - no doubt saves many lives. The diligence of law enforcement means our neighborhoods are safer."

Chad Plantz, special agent in charge of Homeland Security Investigations San Diego, said that fentanyl continues to be the most significant drug-related concern for Homeland Security Investigations "due to its widespread availability, highly addictive features, and deadly effects."

A small pile of cocaine

Aaron Leib Kobisher is also charged with trafficking cocaine. (iStock)

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"The success of this investigation is the result of law enforcement agencies working together to dismantle drug trafficking organizations and holding those accountable for their actions- no matter where they hide."

Experts say the U.S. is currently in a "fourth wave" of opioid overdose deaths, this one marked by a sharp increase in fentanyl — a synthetic opioid — being mixed with stimulant drugs. The current (fourth) wave began in 2015, with the rise in fentanyl mixed with stimulants.

A study published in the journal Addiction on Thursday by UCLA found that the share of overdoses involving a combination of fentanyl and stimulants increased by more than 50-fold — from .6% (235 deaths) to 32.3% (34,429 deaths) — between 2010 and 2015.

Fox News’ Melissa Rudy contributed to this report.