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BEDFORD, Indiana - Justin Lampkins, 25, served his country for four years as a Marine, but it was a shot to his chest in a McDonald's drive-thru line that took his life.

"It's a senseless act to kill somebody over a horn," Bedford Assistant Police Chief Joe DeWees told WTHR. "This is one of the most senseless acts I have ever seen."

DeWees says it started when Lampkins or one of his friends inside his truck honked the horn because the line was not moving.

That's when the person at the front of the line got out of his pickup, went back to Lampkins' vehicle, and punched him, according to police.

Officers say when Lampkins shoved the suspect back, 22-year-old Evan Schaffer fatally shot him in the chest, then raced away from the scene.

Based on a description of Schaffer's vehicle, officers caught up to him and arrested Schaffer for murder.

The Bedford Police Department released surveillance pictures, asking for more information from occupants in the surrounding vehicles.

Officers have since posted on Facebook that all witnesses have now come forward.

Lampkins spent four years as an active duty sergeant at Camp Lejeune in North Carolina.

His brother-in-law says Lampkins was a caring man who would help anyone in need.

"He was the epitome of a Marine, stand up for everybody," Erick Stahl told WTHR. "His whole life was riddled with stories of defending people when they needed it. He was not violent, he did not act like that. He was not an angry or disrespectful person. He's going to be missed."