SAN FRANCISCO -- The parents of a 21-year-old Antioch man who was being trailed by undercover narcotics officers when he was fatally shot by Concord police last May have filed a federal civil rights suit claiming their son was "intentionally and maliciously" killed.

Charles Burns was shot and killed in Antioch by Concord police on May 10, 2013, as he and his friend Bobby Lawrence, 21, of Bay Point, were headed to Walmart to buy a Mother's Day card, according to the lawsuit.

The suit was filed on behalf of Lawrence and Burns' parents, John and Tammie Burns in a San Francisco federal court on Tuesday.

Charles Burns was a drug suspect under police surveillance when he left his home in the 2700 block of Barcelona Circle in Antioch around 9 p.m. and got into a truck driven by Lawrence, authorities said.

When undercover officers attempted to stop the vehicle and serve a warrant on him, Lawrence sped off and was rammed by an unmarked police car, according to the suit. The suit alleges that undercover police, without identification, pointed a gun at the vehicle as it tried to drive away to safety.

Police have said it was actually Lawrence who rammed the unmarked car and that Burns was fatally shot while running from the truck because officers feared for their safety. The suit claims that after the vehicle came to a stop, Burns jogged about 20 feet then stopped in the middle of the street as instructed by police.

"Burns was not armed and carried no weapon or anything that could be construed as a weapon," the complaint reads. "Burns took no aggressive action but rather yielded to the officers. ... Three officers from the Concord Police Department lined up in firing squad execution fashion and unloaded their weapons on the defenseless Burns with full intent to execute him."

Walnut Creek attorney Peter Johnson, who represents the plaintiffs, was not immediately available for comment Thursday.

Concord City Attorney Mark Coon said Thursday that it is the city's standard practice not to comment on pending litigation. The Contra Costa County Coroner's inquest on the death of Burns will be held Thursday in a Martinez courtroom. Inquests are held in fatal incidents involving police officers to present the facts to a jury for their deliberation and determine how the person was killed.

The suit seeks unspecified damages and names the city of Concord and its police department, Chief Guy Swanger, Contra Costa County and its District Attorney's Office, District Attorney Mark Peterson and two police officers. It claims "excessive, unjustified and unreasonable lethal force" was used against Burns, and that police and other authorities acted in a "shroud of secrecy" in the killing of Burns.

Follow Kristin J. Bender at Twitter.com/kjbender.