HOUSTON (AP) — Authorities are trying to determine what motivated a 30-year-old man accused of ambushing a uniformed sheriff's deputy and firing multiple shots in what they believe was a targeted killing.

Shannon J. Miles is charged with capital murder in the fatal shooting Friday night of Matthew Goforth, a 10-year veteran of the Harris County Sheriff's Office.

Harris County Sheriff Ron Hickman says there is no evidence so far that Goforth knew Miles and the attack was "clearly unprovoked."

Hickman says their assumption is that Goforth was targeted because he was in law enforcement, although they have not learned any details from the suspect that would shed light on his motive.

Prosecutors in Texas are charging a 30-year-old man with capital murder in the killing of a sheriff's deputy who was gunned down from behind while filling up his patrol car at a suburban Houston gas station.

Harris County Sheriff Ron Hickman identified the man as Shannon J. Miles, who had a previous record including charges of resisting arrest and trespassing.

Hickman says the motive for the killing had not been determined but investigators would look at whetherMiles, who is black, was motivated by anger over recent killings elsewhere of black men by police that have spawned the "Black Lives Matter" protest movement.

Deputy Darren Goforth, who was 47, was pumping gas Friday night when the gunman approached him from behind and fired multiple shots, continuing to fire after the deputy had fallen to the ground. Goforth, who was white, was a 10-year veteran of the force.

Earlier on Saturday, Hickman had called the killing a "cold-blooded assassination."

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