THORNTON, Colo. (CBS4) – Police in Thornton say a 35-year-old man is under arrest, accused of fatally stabbing his mother and injuring his grandfather in the parking lot of a Chili’s on Thursday evening. Police are not releasing the man’s picture or his name.

Scene of stabbing outside Chili's in Thornton, Colorado

(credit: CBS)

The adult female was killed and the other victim, an adult male, suffered serious injuries and was rushed to the hospital.

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Investigators did not clarify whether the trio was dining at the restaurant before the stabbing happened. The restaurant located at 16507 Washington Street was open to the public before the stabbing. What led up to the stabbing is being investigated.

(credit: CBS)

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There are no other suspects and formal charges have yet to be filed.

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The suspect remains in custody.