Mexican drug lord Joaquin "El Chapo" Guzman has pleaded for U.S. court authorities to transfer him back to his country of birth, court filings showed Monday, as he serves out a life sentence he deemed "cruel."

Extradited in 2017 after escaping twice from Mexican prisons, Guzman is serving a life sentence at a maximum security facility in Colorado on multiple charges including drug trafficking and money laundering.

AFP reviewed three letters the co-founder of the Sinaloa cartel wrote, each one filed on Monday. CBS News also obtained one of the letters, which is written in grammatically incorrect English.

"This is a polite letter (about) the hardcore evidence that wasn't proven for my case," Guzman wrote in the letter, dated April 23.

In the letter directed to the Eastern District Court of New York, Guzman asked that authorities recognize his "rights to be request back (sic) to my country," without clarifying if his request is to serve the rest of his sentence in Mexico.

In another missive on April 20, Guzman complained that his requests for the documents behind his sentencing have gone unanswered.

These documents won't justify "my cruel punishment," he added. "The verdict of my trial wasn't fair," he said.

El Chapo said that he has been waiting for an appeal for three years, and invoked the protection of the "first to the fifth amendment."  

The former trafficker has repeatedly complained in previous prison letters of isolation, poor conditions in his cell and the lack of family visits. In 2023, the Sinaloa cartel founder appealed to then President Andres Manuel Lopez Obrador for help due to alleged "psychological torment" that he said he was enduring in prison.

El Chapo is incarcerated at the "Supermax" prison in Florence, Colorado, which has held a number of high-profile inmates, including Unabomber Ted Kaczynski, Boston Marathon bomber Dzhokhar Tsarnaev, Sept. 11 conspirator Zacarias Moussaoui and Oklahoma City bombing accomplice Terry Nichols. The facility is so secure, so remote and so austere that it has been called the "Alcatraz of the Rockies."

Last month, Mexican soldiers captured three of El Chapo's brother's closest allies in an operation backed by U.S. intelligence. His brother, Aureliano Guzman Loera, known as "El Guano," still has a $5 million U.S. bounty on his head.