Deputies said this investigation has been given high priority.
Video from the confrontation on Sunday night shows the husband of a Harris County Sheriff's deputy being put into the back of a sheriff's car. The sheriff's office only identified him as 41-year-old Thompson.
You can also see the ambulance that was called to the restaurant. Inside that ambulance, paramedics are giving CPR to 24-year-old John Hernandez.
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Security video from the night of the incident shows only a portion of the confrontation. The deputy's husband is seen wearing an orange shirt.
Hernandez's wife said the other person recorded in the video is her husband.
She admits her husband was drinking that night and had gone outside the restaurant to urinate.
Hernandez's family said he was in a coma being kept alive by machines, but died Thursday.
"He was on the floor, and he had him, the other guy had him and he was punching him like this, endlessly," Mrs. Hernandez said.
Deputies said Thompson's wife was off-duty when she arrived at Denny's to meet her family. She called for assistance from the sheriff's office and EMS.
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Deputies said she helped her husband restrain Hernandez and that her husband was only defending himself after he was punched.
Hernandez's family said they want answers from the sheriff's department. An investigation into the incident is currently underway.
No charges have been filed.