EL PASO, Texas (Border Report) – Alleged Sinaloa cartel co-founder Ismael “El Mayo” Zambada on Friday waived a court appearance in El Paso federal court and pleaded not guilty to charges that led to his arrest this week.

Court records show Zambada was scheduled to go before U.S. Magistrate Judge Anne T. Berton at 8 a.m. on Friday to be informed of the charges and instructed of his rights under the American judicial system. However, Dallas-based attorney Frank Perez filed a waiver of appearance and entered a plea of “not guilty” on behalf of his clients, court documents filed U.S. District Court for the District of West Texas show.

Zambada is now scheduled for arraignment — which he can also waive — on July 31 and an Aug. 1 status conference hearing before U.S. District Judge Kathleen Cardone for which he must show up in person. The West Texas drug, conspiracy and running a criminal enterprise charges against Zambada date back to 2012. He also has pending cases in New York, Illinois, the District of Columbia and California.

Zambada and Joaquin Guzman Lopez, son of jailed drug lord Joaquin “El Chapo” Guzman, were arrested Thursday in El Paso, U.S. Attorney General Merrick Garland confirmed.

Garland and Drug Enforcement Administrator Anne Milgram characterized the arrests as a major blow against a transnational criminal organization flooding American communities with the deadly drug fentanyl and other illicit substances that net the cartel billions of dollars in profits.

And while Zambada remains in El Paso, Guzman Lopez was flown out of the city early Friday to face prosecution in Chicago.

How the two major cartel players ended up in El Paso remains a mystery.

The Mexican government on Friday said it did not participate in the arrest or surrender. But its leaders said the U.S. actions are in line with binational cooperation to combat the scourge of fentanyl. They also floated a theory of how the airplane in which they were passengers ended up in the United States.

“Did we participate? No, the Government of Mexico did not take part in this detention or surrender. That is not the case. But we will continue to collaborate as we have done so far,” Mexican Public Safety Secretary Rosa Icela Rodriguez said Friday in a news conference broadcast on YouTube.

Rodriguez showed images of Zambada and Guzman Lopez in U.S. custody.

The secretary said the U.S. Embassy in Mexico notified her office of the apprehensions at 3:30 p.m. Mexico City time on Thursday. She said the embassy later told her the identities of the suspects had been confirmed through fingerprints and other biometric information.

“Part of the investigation is whether this was (an arrest) or a surrender, a pre-arranged surrender,” she said.

Rodriguez also showed a flight plan of a Cessna 205 aircraft that took off from Hermosillo International Airport in Sonora, Mexico, at 8:05 a.m. Thursday heading toward Santa Teresa, New Mexico.

The plan lists an American pilot, Larry Curtis Parker, as the sole occupant. The Cessna was supposed to land in Santa Teresa at 10:19 a.m.

Efforts to contact Parker by Border Report and KTSM were unsuccessful.

KTSM could not verify arrivals to the Doña Ana County Jetport on Thursday afternoon. On the runway, KTSM crews spotted a Beech King Air B200GT which comfortably transports seven passengers as opposed to a Cessna 205, which seats five passengers and a pilot. Witnesses told KTSM that authorities had the Beech King Air surrounded on the runway on Thursday afternoon.

Rodriguez said the pilot is not listed as a U.S. embassy employee or agent, but merely as a visiting pilot flying back to the U.S.

“It is a fact that one left from here, and over there three arrived. We will see what the precise information is in this case,” she said. “The investigation is ongoing in Mexico and in the United States.”

Mexican President Andres Manuel Lopez Obrador was asked to explain the difference between the two airplanes allegedly involved in the arrest of “El Mayo” and the other defendant. The president said that the matter is under investigation.

“They could have changed (airplanes) along the way. We will know that later. Also, one left Hermosillo and three landed (in the U.S.) Did they land and (added passengers)? All of that is under investigation, we’re seeing what the cameras show.”

Lopez Obrador said he would wait to hear from U.S. authorities about the nuances of the arrest and what the airplane situation was. He said he didn’t even know, officially, which U.S. agency placed Zambada and Guzman Lopez under custody.

What happens to the Sinaloa cartel now?

Typically, when a drug lord is arrested or killed in Mexico, a bloody scramble to replace him takes place. Rodriguez said she would not speculate on how the arrests would impact the Sinaloa cartel. “That is speculation. […] We leave the speculation up to you,” she told Mexican news media members who asked the question.

Rodriguez and Lopez Obrador emphasized that Mexico and the U.S. collaborate well on public safety and other common issues. “I would like to emphasize we have good collaboration. If there is a detention (of a foreign national), we notify their embassy,” Rodriguez said.

U.S. authorities previously identified four of the sons of “El Chapo” Guzman as heading one faction of the Sinaloa cartel, with Zambada leading the other. In addition to Joaquin Guzman Lopez, Ovidio Guzman Lopez is also jailed in the U.S. after extradition.

Federal prison records show Ovidio Guzman was released on July 23, but Rodriguez in Mexico said she believes he is still in U.S. custody, but his jail arrangements may have been modified.