Prosecutors have dropped an assault charge against a former Los Angeles County sheriff’s jail guard who was accused of allowing a man to be beaten by other inmates.

The case against Jonathan Grijalva, 29, was dismissed on the first day of trial last week after prosecutors said they could not locate a key witness — the man who had been attacked.

Grijalva, a custody assistant, was working at the North County Correctional Facility in 2014 when an inmate asked him to walk to another area of the lockup so that another man could be assaulted, prosecutors alleged.

The guard at the Castaic lockup was also accused of refusing to arrange for medical care after the targeted inmate, Saul Lira, was beaten by three other men and suffered a broken nose and jaw.

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