An activist stands outside of police headquarters in Los Angeles, Jan. 9, 2015. A county sheriff in Texas Saturday linked the Black Lives Matter movement to the death of Darren Goforth, a sheriff's deputy who was gunned down at a Houston area gas station. Reuters/Mario Anzuoni

Have Black Lives Matter activists and demonstrators helped to cause the death of a U.S. police officer? Texas officials posed that question as they searched Sunday for a motive in the execution-style slaying of Darren Goforth, a white sheriff's deputy in Harris County who was gunned down Friday at gas station, allegedly by a black man.

Shannon Miles, 30, of Cypress, Texas, who has been charged with capital murder in Goforth's death, was expected in court for an arraignment hearing Monday, the Associated Press reported. Authorities accused Miles of ambushing Goforth, 47, as the officer pumped gas at a Chevron station in Cypress, a suburb of Houston.

Ron Hickman, the Harris County sheriff, said Saturday the shooting appeared "unprovoked" and Miles had not provided authorities with information to indicate a motive. However, Hickman stopped just short of blaming Goforth's death on Black Lives Matter, the anti-police brutality movement that has spread throughout the nation in recent years.

"We've heard black lives matter; all lives matter. Well, cops' lives matter too," Hickman said, according to the AP. "At any point where the rhetoric ramps up to the point where calculated cold-blooded assassination of police officers happen[s] -- this rhetoric has gotten out of control," he continued.

Although dozens of officers have died in the year since nationwide protests were sparked by police-involved deaths of unarmed black men in Ferguson, Missouri, and Staten Island, New York, firearms-related law enforcement deaths were down from the same period last year, Reuters reported. Law enforcement deaths overall have increased slightly in the first eight months of 2015, due in large part to traffic accidents, according to the National Law Enforcement Officers Memorial Fund in Washington, which tracks line-of-duty deaths.

"It is unfortunate that Sheriff Hickman has chosen to politicize this tragedy and to attribute the officer's death to a movement that seeks to end violence," Deray McKesson, a purported leader in the Black Lives Matter movement, told the Houston Chronicle.

Shannon Miles, left, and Darren Goforth, right, are pictured. Reuters

Authorities said the gunman who killed Goforth approached him from behind, as the officer refueled his vehicle, and opened fire. The assailant continued to fire even after Goforth had fallen to the ground, Hickman said. "Our assumption is that he was a target because he wore [an officer’s] uniform," he said.

Miles has had several brushes with the law, stretching back to 2005, when he was convicted of criminal mischief, giving false information to police and resisting arrest, the AP reported. In 2006, Miles was convicted of disorderly conduct with a firearm and sentenced to 15 days in jail. His most recent conviction was for resisting arrest in 2009.

Number of People Killed by Police by State in 2015 | FindTheBest