A black suspect who tussled with white deputies as they detained him in a suburb of New Orleans last week died of asphyxiation and there was evidence of pressure on his neck, a coroner said Monday.

The death of Keeven Robinson, 22, has been classified as a homicide based on the preliminary autopsy results, which indicate traumatic neck injuries "consistent with compressional asphyxia," said Jefferson Parish Coroner Gerry Cvitanovich (sih-TAN'-uh-vich). He said complete results, including toxicology reports and examination of microscopic evidence from Robinson's lungs, will take weeks.

"That said, I don't want to delay disclosure regarding the direction in which we're heading from Mr. Robinson's family, the sheriff's department or the media," Cvitanovich said. He added that he had shared the preliminary findings with Robinson's mother prior to his joint news conference with Jefferson Parish Sheriff Joe Lopinto.

Lopinto said Cvitanovich told him of the autopsy report Saturday. He said the four deputies involved in the arrest have been read their rights and are cooperating in an investigation that involves his office, state police and the FBI. All have been placed on administrative duty.

"I understand that this investigation will be under a microscope," Lopinto said.

Hester Hilliard, an attorney for Robinson's family, said the sheriff and coroner have acted with "professionalism and transparency." However, she also said the family would like to see an agency other than the sheriff's office lead the investigation.

New Orleans news outlets reported that more than 100 people took part in a Monday night march to honor Robinson near the scene of his death, in Metairie. Social media video showed some carrying signs. One read "Enough is Enough." Another said "Justice for Keeven."

Some marchers were heard singing "Amazing Grace."

Lopinto declined to immediately identify the deputies. He confirmed they are white. Robinson was black.

"There's no doubt they used force," Lopinto said. "It's whether the force was excessive."

Lopinto said it was too early to conclude whether a choke hold was used. Officers are not expressly forbidden under department policy to use choke holds, but they aren't trained in them either.

"From a policy standpoint, we don't train somebody to hit someone with a brick," Lopinto told reporters. "But if you're fighting for your life and a brick's there, you hit someone with a brick."

Among those attending the news conference was Gaylor Spiller of the Jefferson Parish chapter of the NAACP. She said the organization was supporting Robinson's family and keeping an eye on the case.

She credited Lopinto and Cvitanovich for being open about the autopsy results and the investigation. "We're here to support all sides," Spiller said. "I just want the truth."

News outlets in New Orleans previously cited authorities as saying that Robinson, under surveillance by narcotics agents, drove away from a gas station Thursday morning when he saw agents approaching. He abandoned his car after crashing into two vehicles, then ran from deputies. They caught and handcuffed him in the backyard of a home, the reports said.

Lopinto said Monday that Robinson was unarmed when he was detained. He said there was a gun in Robinson's car and that he had heroin on him.

So far, no video has surfaced. The Jefferson Parish Sheriff's Office doesn't use body cameras. Even if it did, Lopinto said, the deputies involved were undercover detectives.

"Undercover narcotics agents would not have a body camera strapped to their chests," he said.