UPDATE - 5:54 p.m. EST

A suspect was arrested in connection to the shooting of Deputy Darren H. Goforth at a gas station in Houston. Harris County Sheriff Ron Hickman said that Shannon J. Miles is charged with capital murder. The motive remains unclear.

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Houston police are questioning a person of interest who was taken into custody following the fatal shooting of a Harris County sheriff's deputy, who was killed execution-style while he was pumping gas into his patrol car Friday night.

The shooting occurred when 47-year-old Deputy Darren Goforth stopped by a gas station in northwest Harris County around 8:30 p.m. after leaving an accident scene. As he was pumping gas, a man approached him from behind and opened fired without warning or saying a word.

"He was pumping gas into his vehicle and the male suspect came up behind him and shot the deputy multiple times," Harris County Sheriff's Office spokesman Deputy Thomas Gilliland told the Houston Chronicle. "The deputy fell to ground. The suspect came over and shot the deputy again multiple times as he lay on the ground."

Goforth was pronounced dead on the scene.

The person of interest, who has been described as a 20-something-year-old dark complexed male, is being questioned at the Harris County Sheriff's Office in east Houston. Officials have not released his identity.

The man's mother, however, defended her son's innocence, telling Eyewitness News, "My son is innocent. I was in the house with him, so when that happened, my son was home."

A motive has yet to be determined for the shooting.

According to Harris County Sheriff Ron Hickman, the slain deputy was a 10-year veteran of the force with a wife and two children.

"In my 45 years in law enforcement, I can't recall another incident so cold-blooded and cowardly," Hickman said.

"This is a very tough moment right now for the Harris County Sheriff's Office. I can ask you if you give us your prayers and your thoughts," Gilliland added. "It's tough enough being a deputy and being in law enforcement in this country right now, but for people, the way that they are right now, I have no words for what this type of person did."