CHULA VISTA, Calif. - A San Diego man accused of fatally stabbing his estranged wife in a parking lot at a South Bay sheriff's substation pleaded not guilty Friday to a murder charge and was ordered held on $5 million bail.

Marvin Dennis Duncan faces 26 years to life in prison if convicted of killing his 36-year-old wife, Rocio, said Deputy District Attorney Ted Minahan.

Shortly after 3:30 p.m. Wednesday, Duncan pressed an intercom button at a side door at the precinct house on Imperial Beach Boulevard, said sheriff's homicide Lt. Glenn Giannantonio. When a deputy answered, Duncan, who was holding two toddlers, announced he had just killed his spouse, according to the lieutenant.

The mortally wounded victim was found lying on the ground on the west side of the substation. She died a short time later.

Duncan, 59, was detained for questioning and later arrested. The children, who were unharmed, were taken into protective custody. The motive was under investigation.

Duncan will be back in court Feb. 21 for a readiness conference and Feb. 25 for a preliminary hearing.