The bodies of seven people have been found in Joliet, near Chicago, with authorities saying the victims are all thought to be from the same family.
Police said 23-year-old Romeo Nance was wanted and that he was "armed and dangerous". In a statement about the attack, which took place 64 km southwest of Chicago, the Joliet police department said: "Multiple people were found shot to death and he continues his killing spree. This is an active investigation in which we are working with our law enforcement partners in the area."
Will County Sheriff's Chief Deputy Dan Jungles said, "I've been policing for 25 years, and this is probably the worst crime scene I've ever been on duty at. The motive for the attack is not yet clear, but the suspect is believed to have known the victims."
Authorities said one of the shootings resulted in the death of a 28-year-old man shot in the head.