A 16-year-old boy who authorities say set a mattress fire in an apartment building has pleaded not guilty to murder in the death of a New York City police officer who responded to the blaze.

Prosecutors in Brooklyn arraigned Marcell Dockery Wednesday. He faces up to 25 years to life in prison if convicted of killing officer Dennis Guerra.

Defense attorney Jesse Young tells the Daily News his client denies confessing to setting the fire. The newspaper says his family members cried when the charge was read.

Authorities have said Dockery set the fire on the 13th floor of a Brooklyn building because he was bored.

Guerra’s partner remains in critical but stable condition.

In the wake of Guerra’s death, NYPD officials changed protocols for officers responding to fires.

(AP)