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A Rancho Cucamonga man faces potential murder charges after he allegedly fatally assaulted his girlfriend’s daughter while she was left in his care, police said Monday.

The incident took place last Tuesday night, when 24-year-old Adam Hughes was watching his girlfriend’s children, including a 4-year-old girl with Down Syndrome, according to a Rancho Cucamonga Police Department news release.

Hughes became angry at the victim, Kylee Willis, when she interrupted him at some point, the release stated.

He then allegedly assaulted Kylee before putting her to bed.

Hours later, Hughes checked in on the child and found her unresponsive, police said. He saw the girl’s lips and fingers had turned blue.

Hughes then called his girlfriend Corrine Blake, who in turn called 911 for help shortly before 8 p.m., according to the release.

Kylee was first transported to San Antonio Medical Center before being flown to Loma Linda University Medical Center, where she was treated for severe head trauma.

She was placed on life support but ultimately succumbed to her injuries on Friday.

“My daughter Kylee has forever closed her smiling irish eyes, she was taken from this world to soon by the people that we’re sworn to protect her,” her father, Victor Willis, wrote in a GoFundMe page he started to help pay funeral costs.

Hughes and Blake were both arrested last Wednesday and booked on suspicion of willful cruelty to a child, according to police.

Blake posted bail and was released from jail the following day.

On Friday, after Kylee died, Hughes was also booked on suspicion of murder and assaulting a child, according to San Bernardino County inmate records.

He is being held without bail and is expected to appear in court on Tuesday.

Police declined to release his booking photo.

No further information was released amid the ongoing investigation.

Anyone with information about the case is asked to call Detective Wendi Beaton at 909-387-3589. Tips can also be left anonymously through by dialing 800-78-CRIME or visiting the website www.wetip.com.