A Rikers corrections officer, finally arrested Monday for the decade-old murder of his ex-girlfriend, pleaded not guilty to the charge today and was ordered held without bail.

Christopher Clavell, 46, who was picked up in uniform, was remanded for allegedly gunning down Barbara Perez on August 11, 2000, at the gym she worked at in Ridgewood, Queens.

Perez and Clavell were in the middle of a custody battle at the time of the shooting, Clavell had been the only suspect in the case.

It was still unclear as to what lead authorities to the arrest in the 10-year-old cold case.

Clavell — who was put in protective custody in Rikers — faces 25 years to life in prison if convicted.