Police arrested 18-year-old Alex Castanon of West Palm Beach after they said he shot and killed his girlfriend Sunday night.

On Sunday officers got a call at around 10 p.m. in the 600 block of 34th Street in the Old Northwood Historic District. Police said the woman, whose name has not been released, was found lying on the ground outside a house with an apparent gunshot wound to the head.

She was pronounced dead at the scene.

Police said Castanon  admitted to shooting the victim inside the house on 34th Street.

West Palm Beach police spokesman Mike Jachles said the weapon used in the shooting was later recovered several houses away in an alleyway near the scene.

Castanon faces one count of second-degree murder with a firearm. He was booked into the Palm Beach County Sheriff’s Office Main Detention Center where he is being held without bond.

Investigators are still trying to determine a motive for the killing.