Authorities respond to an apparent murder-suicide in Valinda on Sept. 10, 2018. (Credit: KTLA)

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Authorities believe a 64-year-old man fatally shot his nephew and injured his sister before killing himself in Valinda Monday night.

The incident occurred about 7:25 p.m. in the 1800 block of Gretta Avenue, according to the Los Angeles County Sheriff’s Department.

The victims' son and brother apparently saw his uncle shoot the victims before running out and calling 911.

Responding deputies and firefighters found the victims, who were transported to a hospital. The nephew, 18-year-old Ezekiel Griego, was pronounced dead, while his mother, 60-year-old Jeanita Griego, was left in critical condition.

As of Tuesday night, she was on life support, authorities said.

Lt. John Corina told KTLA 64-year-old Thomas Stratton, described as the suspect, apparently shot the victims in the head while they were both seated. He then went into another room and shot himself in the head.

Stratton was pronounced dead from an apparent self-inflicted gunshot wound to the head, according to the Sheriff’s Department.

All three parties lived in the home together, officials said.

The weapon believed to have been used in the triple shooting was found at the scene.

The motive behind the incident is unknown.

Anyone with information about the shooting can call the Sheriff’s Department’s homicide bureau at 323-890-5500.

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