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Homicide investigators planned to release a composite sketch and were seeking surveillance video of a man who fatally attacked a good Samaritan who had prevented a child from potentially being harmed at a Hollywood McDonald’s, police said Friday.

Gabriel Alvarez Ortega Jr., 57, was inside the fast-food restaurant in the 1400 block of Vine Street (map) about 9:30 p.m. June 18, his birthday, when he saw another man yelling at a small child.

The unidentified man had his fists clenched as he walked toward his 3-year-old son, according to the Los Angeles Police Department.

Sensing the child was about to be attacked, Ortega acted as a shield and blocked the father from getting at the young boy.

“Mr. Ortega stood in front of the child and told the individual to leave the child alone,” LAPD Detective Steven Katz said. “When he did this, the individual punched Mr. Ortega in the face and fled on foot.”

Police responded, taking a battery report. Ortega said he would seek medical attention on his own.

Three days later, after suffering headaches and vomiting, Ortega checked into a local hospital, Katz said. He died on July 14.

On Wednesday, the Los Angeles County coroner’s office determined Ortega had died from blunt force trauma from injuries sustained in the incident.

Police called for the public’s help finding the attacker on Thursday.

“You never know who saw this, who knows this person,” Katz said. “We’re looking for any help on this case. This is a tragic incident.”

The assailant was described only as a 30- to 40-year-old African-American male between 5 foot 7 and 5 foot 9.

Police said employees at the McDonald’s, just south of the busy intersection of Vine Street and Sunset Boulevard, were cooperating. Employees said they could not comment.

A neighbor described Ortega as “very happy,” saying he was shocked by his death.

Anyone with information about the incident was asked to call homicide detectives Jose Robledo or Fernando Rivas at 213-382-9470 or, during nonbusiness hours and on weekends, 877-527-3247.

Anonymously tipster may call 800-222-8477, text a message beginning with the letters “LAPD” to 274637, or go to lapdonline.org.