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The killer of a California police officer has died after being found unresponsive in his cell at San Quentin State Prison.

Miguel Magallon, 35, died Saturday despite emergency measures. An autopsy will be conducted, corrections officials said Monday.

Magallon was sentenced to death on Oct. 15, 2009, for the Aug. 10, 2004, murder of Capt. Michael Sparkes Sr. of the Los Angeles County Office of Public Safety.

Prosecutors in the case said Sparkes, 53, was taking his regular predawn bike ride in a neighborhood near his Compton home when Magallon stepped out of a vehicle and tried to rob him. He shot the officer multiple times with an AK-47 before fleeing to a waiting car.

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