Updated

A 15-year-old New Mexico teenager has pleaded not guilty to a murder charge in the killing of his 12-year-old playmate.

The Albuquerque Journal reports (http://bit.ly/Q1n2WQ) a defense attorney entered the plea for the teen during his arraignment Friday afternoon.

Cindy Mercer, the suspect's attorney, says her client's low-functioning mental capabilities make her question whether he understands the proceedings or his rights.

State District Court Judge Violet Otero acknowledged Mercer's concern before setting a $500,000 cash-only bond.

Valencia County Assistant District Attorney Darlene Weed says Alex Madrid of Albuquerque was stabbed repeatedly in the head and suffered a punctured lung.

Prosecutors say the teen stabbed Madrid before placing his body under a mattress in a rural field outside Los Lunas.

They say the suspect will be tried as an adult.

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Information from: Albuquerque Journal, http://www.abqjournal.com