A young black man who died in the custody of four white Louisiana deputies had "significant traumatic injuries" to his neck consistent with asphyxiation, according to the coroner, who classified the case as a homicide.

The Jefferson Parish Sheriff's Office put the four narcotics agents involved in the confrontation on desk duty and asked Louisiana State Police and the FBI civil rights task force to join his investigation of how drug suspect Keeven Robinson, 22, was killed Thursday.

"I understand this incident will be under a microscope," Sheriff Joseph Lopinto said at a Monday news conference where the preliminary results of this weekend's autopsy were announced.

An attorney for Robinson's family, Hester Hilliard, said the autopsy result compounded their grief.

"They had to find out Keeven lost his life at the hands of another, and that's very, very hard for them," she said. "And now they have to move on to making funeral arrangements for this 22-year-old, who should not have died."

Hours later, Robinson's family led more than 200 neighbors on a march past the spot where her only son died.

"They're killing the children," Robinson's grandmother, Sheryl, told reporters. "Enough is enough."

Robinson, who was the target of an undercover drug operation, fled from police in his car, crashed into two sheriff's vehicles, and then fled on foot — jumping over several backyard fences before he was caught with drugs on him, officials said.