TEANECK — Prosecutors have upgraded the criminal charges against a father from the Bronx who is accused of mercilessly beating his twin infants, who lived with their mother in Bergen County.

One of the babies, who spent days in the hospital fighting for life, ultimately died on Thursday.

Jonathan Melendez, 27, was arrested last Friday at Hackensack University Medical Center two days after the mother of the babies had brought them to the emergency room.

One of the infants was unconscious, authorities said. The hospital notified law enforcement after realizing that the babies had several broken bones and serious head injuries.

Prosecutors said Melendez was caring for the children at the time that they were injured. He was charged last week with second-degree aggravated assault and second-degree child endangerment.

After the death Thursday of one of his children, he was charged with one count of first-degree aggravated manslaughter.

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