When Southern Illinois University student Pravin Varughese was found dead in 2014 after being missing for five days, authorities in Carbondale initially declared it as a tragic accident.
Mr Varughese's cause of death at that time was reported as environmental hypothermia, Chicago Tribune reported.
The family of the 19-year-old student from Morton Grove was simply unwilling to accept that.
His relatives pushed for further investigation, had an independent autopsy performed that conflicted with the local coroner's findings and filed a suit against Carbondale and its police chief, who was fired soon after.
A 12-person jury on Thursday found Gaege Bethune, a southern Illinois man, guilty of Mr Varughese's first-degree murder.
"Pravin's day finally came. He can rest in peace now," Mr Varughese's mother, Lovely Varughese said.
During investigations, Bethune, who was 19 at the time, told police that he gave Mr Varughese a ride on the night of February 12, 2014 after a party, and the two drove around while Mr Varughese was allegedly looking to buy cocaine.
The prosecution said the two had been fighting over money, and alleged Bethune landed several punches to Mr Varughese's head and face that led to Mr Varughese running into the woods, where he later died.
Jurors deliberated for seven hours before returning a verdict, according to WSIL.
They found Bethune guilty of one count of murder that hinged on the state arguing Bethune caused great bodily harm to Mr Varughese and that his death was "a direct and foreseeable consequence," The Southern Illinosian reported.
He was found not guilty on a second murder charge that accused Bethune of robbing the victim, according to the newspaper.
Bethune now faces 20 to 60 years in prison. A sentencing has not yet been scheduled.