Angelica Castro, 21, pleaded guilty to second-degree murder on Thursday.
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Police arrested her in January 2018 after doctors found suspicious injuries on her 5-month-old daughter.
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When officers initially questioned Castro, she claimed she might have accidentally hit the child while they were sleeping.
The doctor who tried to revive the baby later testified that a CAT scan showed the infant had multiple brain bleeds and skull fractures.
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Castro will be sentenced in May. She faces 15 years to life in prison.