Nicholas Sheley has pleaded not guilty to killing 29-year-old Brock Branson; 20-year-old Kilynna Blake; her son, 2-year-old Dayan; and 25-year-old Kenneth Ulve in Rock Falls in June 2008.
The Rock Island Argus reports that jurors began deliberations just before 4 p.m. Thursday.
The 34-year-old Sheley is serving life sentences for killing two other Illinois men and faces trial in two Missouri deaths.
Earlier Thursday a prosecutor said Sheley had left his own DNA in the apartment.
Sheley’s ex-wife also testified the two had sex the day of the killings in a truck cab covered in blood.