Ben Crump told a news conference at Rainbow PUSH headquarters in Chicago that the Justice Department must step in and investigate Day's death as urgently as it has probed cases of suspected foul play involving white victims, such as Gabby Petito.
Crump, who is Black, gained prominence by representing the family of George Floyd and others who were the victims of police brutality and vigilante violence.
“We will make him a priority,” Crump said Friday. "...There is a killer out there on the loose of this young Black man and we need to find him.”
A coroner determined in October that Day died from drowning, but said it was unclear how the 25-year-old had gone into the Illinois River, 60 miles (97 kilometers) north of Bloomington, where he was last seen.
LaSalle County's coroner said an autopsy on Day found no evidence of “manual strangulation, an assault or altercation, sharp, blunt or gunshot injury."
Authorities have said his death remains under investigation. But Day's mother, Carmen Bolden Day, said law enforcement officials have all but told her they believe her son died by suicide, which she dismissed out of hand. She said her son was not depressed or overburdened, had no school-related financial troubles and was studying speech pathology at Illinois State with aspirations of becoming a doctor.
“I’m not the first mother who has lost a child, but when you lose a child and don’t know why … you cannot stop insisting that the people who have made pledges to protect and serve find the answers for you," Day said during the event, where she spoke with defiance and persistence, then wept in Crump's arms.
Jelani Day was last seen Aug. 24 in Bloomington, sister city to Normal, where Illinois State is located. Day's family in Danville and a faculty member reported him missing after he failed to show up for class for several days.
Day's car was found in a wooded area of Peru two days later and his body was discovered in the Illinois River on Sept. 4 in the LaSalle-Peru area. There was no reason for Day to be in LaSalle County, his mother said, and because he suffered no injury before he drowned, she questions how he got into the river.
The LaSalle County Sheriff’s Department announced last month that Day's cellphone had been found and sent to the FBI for forensic testing.
“We want to know what was on his cellphone, we want to know what was his last call, what was his last ping, where he was last seen," Crump said.
In addition to Floyd, Crump has represented the families of Trayvon Martin, Michael Brown and Breonna Taylor, among others.