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CHICAGO (AP) — The mother of an Illinois State University graduate student who vanished in August and was later found dead in a river has hired a prominent civil rights attorney to investigate the Black man’s death.

A coroner determined in October that Jelani Day died from drowning, but said it was unclear how the 25-year-old had gone into the Illinois River. LaSalle County’s coroner said an autopsy on Day found no evidence of “manual strangulation, an assault or altercation, sharp, blunt or gunshot injury.”

In a news release Thursday announcing her hiring of attorney Ben Crump, Carmen Bolden Day said she believes her son was “murdered” and she wants to know who is responsible and why it happened.

Authorities have said his death remains under investigation.

Carmen Bolden was scheduled to join Crump and the Rev. Jesse Jackson at a Friday news conference in Chicago to discuss Crump’s hiring and his efforts to investigate her son’s death.

“Ben feels Jelani is also his brother, and he wants to help find more answers and so do I,” Carmen Bolden Day said in the news release sent by Jackson’s publicist.

She has said her son wanted to become a doctor and was pursuing a master’s degree in speech pathology at Illinois State. He was last seen on the Normal, Illinois, campus on Aug. 24. 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 Peru, Illinois, two days later about 60 miles (96 kilometers) north of Bloomington, and his body was discovered in the Illinois River on Sept. 4 in the LaSalle-Peru area.

The LaSalle County Sheriff’s Department announced last month that Day’s cell phone had been found and sent to the FBI for forensic testing.

Crump, who is Black, has gained national prominence representing victims of police brutality and vigilante violence. He has represented the families of George Floyd, Trayvon Martin, Michael Brown and Breonna Taylor, among others.