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A 17-year-old and two men accused of shooting and killing a Downey police officer last year pleaded not guilty Friday to criminal charges.

Officer Ricardo Galvez, 29, was shot and killed in an attempted robbery Nov. 18 as he sat in his car outside department headquarters. Shortly after, police arrested Steven Knott, 18; Jeremy Anthony Alvarez, 21; and Abel Diaz, 17, in connection with his death.

The three are each charged with one count of special circumstance murder and one count of attempted second-degree robbery. The murder count includes the special circumstance allegation of murder during an attempted robbery.

Galvez had just returned from a police dog-training session a mile away — he was not wearing his uniform and didn’t have his gun on him — when he was killed. A Downey patrol officer pursued a Nissan leaving the parking lot north to Montebello.

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