Suspect extradited from Mexico pleads not guilty in 2018 Midway-area slaying

Ernesto Castellanos Martinez is accused of killing another man on Feb. 25, 2018, outside a 24 Hour Fitness.
(Courtesy of San Diego County Crime Stoppers)

A man who authorities allege fled to Mexico after fatally shooting another man two years ago outside a gym near the Midway District pleaded not guilty to murder and other charges May 6 after being extradited to the United States.

Ernesto Castellanos Martinez, 44, is accused of killing Alexander Mazin, 27, on Feb. 25, 2018, outside the 24 Hour Fitness at Midway Drive and Kemper Street.

“He faces life in prison without the possibility of parole if convicted,” District Attorney Summer Stephan’s office said in a statement.

Jerome Agnew, an off-duty San Diego County sheriff’s deputy who lived in the area, said at the time that he heard two gunshots that sounded like firecrackers and went to his patio. From there, he saw a gunman chasing two men across a nearby parking lot.

“I didn’t see the gun until he exposed it,” Agnew told OnSceneTV. “And then, once he got to the cars on the other side of the parking lot, one of the ... males fell down … and the suspect set up on top of the guy and shot him.”

Mazin died at the scene, according to police.

Later that day, San Diego SWAT officers surrounded a building in North Park where the suspect was believed to be holed up. But when the tactical team obtained a warrant and entered an apartment in the building hours later, the suspect was not inside.

Police were in a standoff with a homicide suspect at an apartment in North Park.

According to the San Diego County District Attorney’s Office, Martinez fled to Mexico and remained there a little more than two years, until his capture and extradition in March.

Jail records showed Martinez, who also went by Ernesto Castellanos, was booked March 14 into San Diego Central Jail on suspicion of murder and felony stalking.

Authorities said Martinez’s arraignment was delayed more than seven weeks due to coronavirus-related court closures.

Police have not released a possible motive in the killing, but in 2018 the victim’s parents reportedly said their son had been going out with a woman Martinez previously dated and that Martinez was alleged to have assaulted the woman weeks before Mazin’s slaying. Jail records showed Martinez also was booked on suspicion of misdemeanor domestic battery.

San Diego County Crime Stoppers offered $1,000 for information leading to Martinez’s arrest, and Mazin’s friends and family put up an additional $8,000 reward.

Martinez reportedly was a mixed martial arts and boxing coach. A photo of him released by Crime Stoppers showed him posing shirtless in a fighting stance at a Midway District mixed martial arts gym.

Stephan’s office offered no details about where or how Martinez was found, saying only that the office’s extradition unit brought him back from Mexico “with the help of law enforcement partners in Mexico, the U.S. Marshals Service and the San Diego Police Department.”


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