“Our officers were read their rights, they cooperated, they gave statements,” Sheriff Lopinto said. “I understand that at the end, this investigation will be under a microscope. I understand it fully.”

Sheriff Lopinto, who declined to identify the detectives who are subjects of the inquiry, reached his decision to reassign the deputies after the parish’s coroner classified Mr. Robinson’s death as a homicide. The ruling — a medical judgment, not a legal one — reverberated loudly through the New Orleans region. More than 100 people protested on Monday evening in Jefferson Parish, among the most populous Louisiana parishes.

The coroner, Dr. Gerald Cvitanovich, said the findings of his office’s preliminary autopsy were that Mr. Robinson’s death was “consistent with compressional asphyxia.” A final autopsy report is not expected for several weeks.

Louisiana has had particularly tense debates about police conduct and race in recent years. Mr. Robinson’s death came less than three months after the Louisiana authorities declined to charge two Baton Rouge police officers in connection with the fatal shooting of Alton B. Sterling in July 2016. Federal prosecutors have also refused to bring charges in that case, which led to large protests in Baton Rouge, the state capital.

In Jefferson Parish this week, civil rights activists welcomed the inquiry into Mr. Robinson’s death. Gaylor A. Spiller, the president of the local N.A.A.C.P. chapter, said she was “so far satisfied” with the coroner’s review and the sheriff’s decision to reassign the deputies.