Fourteen marines were killed Friday when a navy helicopter that supported the operation to capture drug lord Rafael Caro Quintero crashed in Los Mochis, Sinaloa.

One other marine was seriously injured and taken to hospital for treatment. The navy said in a statement that the cause of the Black Hawk helicopter accident hadn’t been established.

“Investigations will be carried out to determine the reasons that may have caused the accident [but] it’s important to clarify that there is no information at this time that [indicates] that the air accident is related to the arrest of the alleged drug trafficker.”

President López Obrador expressed his regret about the deaths of the 14 marines on social media. “I send my most sincere condolences and a hug to their families, colleagues and friends,” he wrote.

The crash occurred after Caro Quintero, founder of the now-defunct Guadalajara Cartel, was captured in Choix, a municipality in northern Sinaloa on the border with Chihuahua. The narco had been sought since 2013, when he was released from prison after serving 28 years of a 40-year sentence for the 1985 murder of United States DEA agent Enrique “Kiki” Camarena.

He was taken into custody early Friday afternoon after a navy dog called Max found him hiding in bushes. Caro Quintero was later transferred to the Altiplano maximum security prison in México state. He is set to be extradited to the United States, where he is wanted for the kidnapping and murder of Camarena and other drug-related crimes, according to his DEA profile.

Along with fellow Guadalajara Cartel leaders Miguel Ángel Félix Gallardo and Ernesto Fonseca Carillo, Caro Quintero was a major supplier of narcotics to the United States in the late 1970s and early ’80s. The U.S. had offered US $20 million for information leading to his capture, but was not directly involved in the operation that ultimately led to his arrest.

With reports from Reforma