The 34-year-old Chicago man was identified to the Lake County Coroner's Office as Joseph McHaney.
RELATED: Armed robber found dead in Lindenhurst home, other alleged robber charged, police say
He and Michael Zachery, 23, of north suburban Evanston, went to a home in the 300-block of Teal Road to purchase a firearm early Tuesday morning, according to the Lake County Sheriff's Department.
Shortly after arriving and speaking to the man selling the firearm, McHaney and Zachery allegedly tried to rob the victim and beat him with a hammer. The victim managed to shoot McHaney, killing him, authorities said.
Someone in the home called 911, but police did not say who made the call. Responding officers found McHaney dead and Zachery being held by a resident of the home.
Zachery was arrested and charged with first-degree murder and armed robbery, for his involvement in an incident resulting in death. He is due in court Wednesday.
Autopsy results showed McHaney died from injuries caused by gunshots, Lake County Coroner Dr. Howard Cooper said. Toxicology results are pending.
The man who shot McHaney was treated at a local hospital and released Tuesday.
The Lake County Major Crime Task Force and the coroner's office are investigating.