CHICAGO — A 16-year-old Chicago boy is accused of fatally shooting a 65-year-old man and his grandson earlier this week, authorities said.

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The teen, who has not been identified, was arrested on Friday and charged on Saturday with two counts of first-degree murder, WGN-TV reported.

The boy is accused of fatally shooting Mario Medina and his grandson, Juan A. Medina Jr., 14, in the Chicago Lawn neighborhood of the city on Dec. 12, according to the Chicago Police Department.

Both victims were standing outside in the 3500 block of West 61st Place just before 4:30 p.m. CST when two gunmen inside a gray vehicle opened fire, the Chicago Tribune reported.

Police said Juan Medina died at the scene, according to the newspaper. Mario Medina was taken to Advocate Christ Medical Center, where he was later pronounced dead.

“There was some type of altercation here. Some individual came to visit another individual, gray car pulled up; they discharged that weapon, striking the 14-year-old,” crisis responder and victim advocate Andrew Holmes told WLS-TV. “We don’t know if he knew the individuals or what was the relationship between the people that was coming to visit him, just don’t know.”

It was unclear whether the other suspect involved in the shooting has been arrested, WFLD-TV reported.

An investigation is ongoing.