A California man is facing a murder charge in the fatal beating of a girl with Down syndrome.

According to the San Bernardino Sheriff's Department, Adam Hughes, 24, of Rancho Cucamonga, was watching girlfriend Corrine Blake's children on March 26 when her 4-year-old daughter, Kylee Willis, "angered Hughes by interrupting him."

"Hughes assaulted Willis and then put her to bed," the Sheriff's Department said in a news release. "Several hours later, Hughes noticed Willis was non-responsive, she had blue fingers and lips."

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Authorities said Hughes then called Blake, who called 911. Willis, who had suffered head trauma, died in the hospital three days later, officials said.

Police initially arrested Hughes and Blake on willful child cruelty charges but later charged Hughes with murder. He has pleaded not guilty, KABC-TV reported.

A toddler boy who also was in the home is now in the care of Children and Family Services, KABC reported.

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